Support installing through a custom GitHub Action (#48)

Signed-off-by: Juan Cruz Viotti <[email protected]>

README.markdown

@@ -38,6 +38,20 @@ powerful [JSON Toolkit](https://github.com/sourcemeta/jsontoolkit) library.
 brew install intelligence-ai/apps/jsonschema
 ```
 
+### From GitHub Actions
+
+```yaml
+- uses: intelligence-ai/[email protected]
+```
+
+Where `X.Y.Z` is replaced with the desired version. For example:
+
+```yaml
+- uses: intelligence-ai/[email protected]
+# Then use as usual
+- run: jsonschema fmt path/to/schemas --check
+```
+
 ### Using the install script helper
 
 ```sh

action.yml

@@ -0,0 +1,10 @@
+name: JSON Schema CLI
+description: Install the JSON Schema CLI
+runs:
+  using: composite
+  steps:
+    # TODO: Install from the latest tag at or before the current commit sha
+    - name: Install the JSON Schema CLI (latest)
+      shell: bash
+      run: |
+        /bin/sh -c "$(curl -fsSL https://raw.githubusercontent.com/intelligence-ai/jsonschema/main/install -H 'Cache-Control: no-cache, no-store, must-revalidate')"