[PATCH] SubmittingPatches: mention doc-diff

[Jeff King <peff@peff.net>]

We already advise people to make sure their documentation
formats correctly. Let's point them at the doc-diff script,
which can help with that.

Let's also put a brief note in the script about its purpose,
since that otherwise can only be found in the original
commit message. Along with the existing -h/usage text,
that's hopefully enough for developers to make use of it.

Signed-off-by: Jeff King <peff@peff.net>
---
Just a finishing touch on the jk/diff-rendered-docs topic.

 Documentation/SubmittingPatches | 4 +++-
 Documentation/doc-diff          | 8 ++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/Documentation/SubmittingPatches b/Documentation/SubmittingPatches
index b44fd51f27..ec8b205145 100644
--- a/Documentation/SubmittingPatches
+++ b/Documentation/SubmittingPatches
@@ -80,7 +80,9 @@ GitHub-Travis CI hints section for details.
 
 Do not forget to update the documentation to describe the updated
 behavior and make sure that the resulting documentation set formats
-well. It is currently a liberal mixture of US and UK English norms for
+well (try the Documentation/doc-diff script).
+
+We currently have a liberal mixture of US and UK English norms for
 spelling and grammar, which is somewhat unfortunate.  A huge patch that
 touches the files all over the place only to correct the inconsistency
 is not welcome, though.  Potential clashes with other changes that can
diff --git a/Documentation/doc-diff b/Documentation/doc-diff
index f483fe427c..6e285e648c 100755
--- a/Documentation/doc-diff
+++ b/Documentation/doc-diff
@@ -1,4 +1,12 @@
 #!/bin/sh
+#
+# Build two documentation trees and diff the resulting formatted output.
+# Compared to a source diff, this can reveal mistakes in the formatting.
+# For example:
+#
+#   ./doc-diff origin/master HEAD
+#
+# would show the differences introduced by a branch based on master.
 
 OPTIONS_SPEC="\
 doc-diff [options] <from> <to> [-- <diff-options>]
-- 
2.19.0.rc0.398.g138a08f6f6