Document differences between version and version_file

Add to the documentation that version_file and release_file cannot be used to generate an output with the N-V-R.A naming scheme.

Fixes #5522.
Closes #5555.

PiperOrigin-RevId: 203946762

tools/build_defs/pkg/rpm.bzl

diff --git a/tools/build_defs/pkg/rpm.bzl b/tools/build_defs/pkg/rpm.bzl
index f3e0064..38f8b26 100644
--- a/tools/build_defs/pkg/rpm.bzl
+++ b/tools/build_defs/pkg/rpm.bzl
@@ -174,7 +174,10 @@
 Two outputs are guaranteed to be produced: "%{name}.rpm", and
 "%{name}-%{architecture}.rpm". If the "version" and "release" arguments are
 non-empty, a third output will be produced, following the RPM-recommended
-N-V-R.A format (Name-Version-Release.Architecture.rpm).
+N-V-R.A format (Name-Version-Release.Architecture.rpm). Note that due to
+the fact that rule implementations cannot access the contents of files,
+the "version_file" and "release_file" arguments will not create an output
+using N-V-R.A format.
 
 Args:
   spec_file: The RPM spec file to use. If the version or version_file