Apply suggestion from @hugovk

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

Author: brettcannon

getting-started/setup-building.rst

@@ -1226,6 +1226,7 @@ Note that the container has read/write access to the working directory.
 You may want to use a separate clone of CPython, or run ``make clean``
 to remove caches and build output generated for your host OS.
 
+.. _building-the-container-locally
 .. _devcontainer-build:
 
 Building yourself