Update README with Publishing section

[shazron]

File: https://github.com/adobe/gatsby-theme-parliament/blob/main/README.md

[shazron]

This will contain:

1. The Pull Request approval flow

• label: deploy or deploy:dev
• PR has to be approved
• PR branch needs to be on same repo (GH security restriction)

2. GH Actions: Site Build: for the GH Contributors component:

• need to standardize on main branch (not master)
• src/pages based off the root of the repo (so we don't set the REPO_ROOT env var)
• set the appropriate env vars as specified in the README

3. GH Actions: Site Build: for the Feedback component:

• set an Org secret for the GATSBY_LAUNCH_URL

4. GH Actions: Azure Blob Storage Deployment:

• set Org secrets for all the Azure Storage connection string for both Prod and Dev
• Azure Container name will just be the repo name (Azure Blob Storage Container is analogous to Folder in S3)

5. GH Actions: Github Pages Deployment:

• no change, except for the new env vars for the 2 components for a Site Build, see above

6. After successful deployment, post a PR comment showing the Azure Static Website Url
7. Update our CDN with the proper mapping to this Azure Static Website Url (needs to be done only once). This is a manual process.