gn: Point to process_version_rc_template() from process_version()'s docs

The documentation for process_version()'s |template_file| argument was
outdated and corresponded to a previous iteration of
https://codereview.chromium.org/2341673003

Update the docs and point to where the rc_template template currently
is.

R=brettw@chromium.org,dpranke@chromium.org

Review-Url: https://codereview.chromium.org/2350953006
Cr-Original-Commit-Position: refs/heads/master@{#419818}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 73326001a1ce814fef68e64b28dc2f17fdcc18a8

util/process_version.gni

@@ -25,8 +25,9 @@
 #     "_version.rc" to the end. But in GN you need to specify the full name.
 #
 #   template_file (optional):
-#     Template file to use (not a list). Most Windows uses for generating
-#     resources will want to use process_version_rc_template() instead.
+#     Template file to use (not a list). Most Windows users that want to use
+#     this to process a .rc template should use process_version_rc_template(),
+#     defined in //chrome/process_version_rc_template.gni, instead.
 #
 #   extra_args (optional):
 #     Extra arguments to pass to version.py. Any "-f <filename>" args should