Add Community Friends page to docs site (#2261)

Move the Community Friends section from the main README into a dedicated
docs page at docs/community/friends.md, following the same structure as
the Reference section.

- New: docs/community/friends.md with content from README
- Updated: docs/toc.yml with Community section and Friends entry
- Updated: docs/docfx.json to include community/*.md in content glob
- Updated: README.md to link to the new docs page instead of inline list

docs/docfx.json

@@ -5,6 +5,7 @@
         "files": [
           "*.md",
           "toc.yml",
+          "community/*.md",
           "reference/*.md"
         ]
       },