Documentation issue: Command-Line Reference

Documentation URL: https://docs.bazel.build/versions/master/command-line-reference.html

The entry for `--workspace_status_command` says:
_A command invoked at the beginning of the build to provide status information about the workspace in the form of key/value pairs. See the User's Manual for the full specification. Also see tools/buildstamp/get_workspace_status for an example._

Two problems:

1. the example is not explaining how it interacts with --workspace_status_command
2. This "manual", what is it? It's definitely not https://docs.bazel.build/versions/4.0.0/command-line-reference.html, and there is no other "manual" anywhere else in the docs.bazel.build hierarchy!

Start with the --workspace_status_command entry in the command-line reference at the documented URL, then inspect tools/buildstamp/get_workspace_status and the references to the User's Manual mentioned there. Done means the example's interaction is explained and the ambiguous manual reference is identified or corrected in the documentation.

Written by the indexing model from the issue text.