Enhance Accelerator documentation for Git

[oZakari]

Overview/Summary

There needs to be more explicit steps for getting the remote repositories synced after initializing the local repository. There also needs to be more specific steps for authenticating to the remote repositories.

AB#29779

Update Accelerator docs after meeting with @paulgrimley

This PR fixes/adds/changes/removes

1. Improves documentation around git commands to make it more seamless for the user if they lack familiarity with git.
2. Adds more specific documentation around the potential authentication methods to Azure DevOps and GitHub repositories.

Breaking Changes

1. None, just documentation changes

Testing Evidence

N/A

As part of this Pull Request I have

• Read the Contribution Guide and ensured this PR is compliant with the guide
• Ensured the resource API versions in .bicep file/s I am adding/editing are using the latest API version possible
• Checked for duplicate Pull Requests
• Associated it with relevant GitHub Issues
• (ALZ Bicep Core Team Only) Associated it with relevant ADO Items
• Ensured my code/branch is up-to-date with the latest changes in the main branch
• Performed testing and provided evidence.
• Updated one or more of the following tests (if required)
  • Unit
  • Linting
  • E2E (End-To-End)
  • ValidateAzCloud (Base validation in Azure Cloud)
  • ValidateMcCloud (Base validation in Azure China Cloud)
• Updated relevant and associated documentation (e.g. Contribution Guide, Module READMEs, Wiki Docs etc.)
• If relevant, created or updated Code Tours here