Add forked repo check and readme not

Author: nginx-jack

.github/workflows/docs-build-push.yml

@@ -50,7 +50,26 @@ env:
   DOMAIN_PROD: "docs.nginx.com"
 
 jobs:
+  checks:
+    name: Checks and variables
+    runs-on: ubuntu-22.04
+    permissions:
+      contents: read
+    outputs:
+      forked_workflow: ${{ steps.vars.outputs.forked_workflow }}
+    steps:
+      - name: Checkout Repository
+        uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332 # v4.1.7
+
+      - name: Set Variables
+        id: vars
+        run: |
+          echo "forked_workflow=${{ (github.event.pull_request && github.event.pull_request.head.repo.full_name != github.event.pull_request.base.repo.full_name) || !(startsWith(github.repository, 'nginx/') || startsWith(github.repository, 'nginxinc/')) }}" >> $GITHUB_OUTPUT
+      - name: Output variables
+        run: |
+          echo forked_workflow: ${{ steps.vars.outputs.forked_workflow }}
   build:
+    needs: [checks]
     runs-on: ubuntu-latest
     env:
       # Remapping of inputs to envs

README.md

@@ -22,6 +22,9 @@ _note: autodeploy from branch is currently in progress. This docs will be update
 
 ## Usage
 
+_note: This action **will not work** with forked Pull Requests. Github does not allow secrets to be shared with forked Pull Requests. Secrets are required as part of Azure interactions. The "Checks and variables" job stops this action running
+and forked requests._
+
 ### Security considerations
 `AZURE_CREDENTIALS` need to contain service principal credentials with the following roles assigned;
 - **Storage Blob Data Contributor**