docs: fixup link to bazel-gazelle (#4392)

**What type of PR is this?**

Documentation

**What does this PR do? Why is it needed?**

bazel-contrib/bazel-gazelle#2125 renamed a file.

**Which issues(s) does this PR fix?**

N/A

**Other notes for review**

Author: dougthor42

README.rst

@@ -48,7 +48,7 @@ Go rules for Bazel_
 .. _go_proto_compiler: proto/core.rst#go_proto_compiler
 .. _go_proto_library: proto/core.rst#go_proto_library
 .. _go_register_toolchains: go/toolchains.rst#go_register_toolchains
-.. _go_repository: https://github.com/bazelbuild/bazel-gazelle/blob/master/repository.md#go_repository
+.. _go_repository: https://github.com/bazelbuild/bazel-gazelle/blob/master/reference.md#go_repository
 .. _go_rules_dependencies: go/dependencies.rst#go_rules_dependencies
 .. _go_source: docs/go/core/rules.md#go_source
 .. _go_test: docs/go/core/rules.md#go_test