docs: rewrite README for aggregation-based architecture

Replaces outdated submodule-based documentation with current
aggregation pipeline using metanorma-release.

Also fix CI debug step to use _site/docs instead of _site/cc.

Author: ronaldtse

.github/workflows/build_deploy.yml

@@ -65,7 +65,7 @@ jobs:
         if: ${{ github.ref != 'refs/heads/main' }}
         run: |
           ls -al _site
-          ls _site/cc | head -20
+          ls _site/docs | head -20
           ls _site/relaton 2>/dev/null || echo "(no relaton dir)"
 
       - name: Upload Pages artifact