Handle a special case "index.md"

[kenji-miyake]

Resolves #24

~/ghq/github.com/autowarefoundation/autoware-documentation add-documentation-tree-structure
❯ ~/ghq/github.com/autowarefoundation/autoware-github-actions/deploy-docs/create-doc-comment.sh https://autowarefoundation.github.io/autoware-documentation/pr-14/ tier4/proposal
::set-output name=comment-body::Documentation URL: https://autowarefoundation.github.io/autoware-documentation/pr-14/
Modified URLs:
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/coding-guidelines/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/coding-guidelines/languages/cmake/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/coding-guidelines/languages/cpp/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/coding-guidelines/languages/github-actions/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/coding-guidelines/languages/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/coding-guidelines/languages/markdown/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/coding-guidelines/languages/package-xml/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/coding-guidelines/languages/python/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/coding-guidelines/languages/shell-scripts/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/coding-guidelines/ros-nodes/class-design/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/coding-guidelines/ros-nodes/console-logging/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/coding-guidelines/ros-nodes/coordinate-system/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/coding-guidelines/ros-nodes/directory-structure/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/coding-guidelines/ros-nodes/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/coding-guidelines/ros-nodes/launch-files/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/coding-guidelines/ros-nodes/naming/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/coding-guidelines/ros-nodes/parameters/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/coding-guidelines/ros-nodes/task-scheduling/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/coding-guidelines/ros-nodes/topic-namespaces/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/discussion-guidelines/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/documentation-guidelines/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/pull-request-guidelines/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/contributing/testing-guidelines/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/design/ad-api/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/design/component-interfaces/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/design/configuration-management/development-process/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/design/configuration-management/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/design/configuration-management/release-process/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/design/configuration-management/repository-structure/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/design/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/help/docs-guide/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/help/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/help/support-guidelines/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/how-to-guides/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/installation/autoware/docker-installation/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/installation/autoware/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/installation/autoware/local-installation/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/installation/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/installation/tools-for-developers/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/installation/tools-for-users/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/tutorials/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/tutorials/local-simulation/closed-loop-simulation/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/tutorials/local-simulation/e2e-simulation/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/tutorials/local-simulation/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/tutorials/local-simulation/open-loop-simulation/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/tutorials/scenario-simulation/closed-loop-simulation/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/tutorials/scenario-simulation/e2e-simulation/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/tutorials/scenario-simulation/
- https://autowarefoundation.github.io/autoware-documentation/pr-14/tutorials/scenario-simulation/open-loop-simulation/