[doc] Add guidance to github notes on adding Signed-off-by lines
This includes guidance on how to add a hook to append the line for you.
Signed-off-by: Alex Bradbury <asb@lowrisc.org>
diff --git a/doc/ug/github_notes.md b/doc/ug/github_notes.md
index 3dfac05..565cf62 100644
--- a/doc/ug/github_notes.md
+++ b/doc/ug/github_notes.md
@@ -94,11 +94,11 @@
The status will initially indicate there are no changes, but as you
add, delete or edit files it will let you know the state of things.
-Once you are happy with your changes, commit them to the local repo by adding the files to the changes (if things are clean you can add using `git commit -a` instead of a number of `add` commands):
+Once you are happy with your changes, commit them to the local repo by adding the files to the changes (if things are clean you can add using `git commit -a -s` instead of a number of `add` commands):
```console
$ git add...
-$ git commit
+$ git commit -s
```
The commit will make you add a message. The first line of this is a
@@ -118,6 +118,9 @@
verification engineers, it should not close the related issue. In this case,
write `Related to #nn` in the commit message rather than `Fixes #nn`.
+The commit message will end with a "Signed-off-by" line inserted by `git` due to using the `-s` option to `git commit`.
+Adding this line certifies you agree to the statement in [CONTRIBUTING.md](https://github.com/lowRISC/opentitan/blob/master/CONTRIBUTING.md), indicating your contribution is made under our Contributor License Agreement.
+
When you have finished everything locally (it is good practice to do a
status check to ensure things are clean) you can push your branch (eg
forchange) to **your** GitHub repo (the **origin**):
@@ -172,6 +175,24 @@
$ git push -f origin HEAD
```
+## Automatically adding a Signed-off-by line for your commits
+
+One option to avoid having to remember to add `-s` to `git commit` is to configure `git` to append it to your commit messages for you.
+This can be done using an executable hook.
+An appropriate hook can be installed by executing this from the root of your repository checkout:
+
+```console
+$ cat <<"EOF" > .git/hooks/prepare-commit-msg
+#!/bin/sh
+
+# Add a Signed-off-by line to the commit message if not already present.
+git interpret-trailers --if-exists doNothing --trailer \
+ "Signed-off-by: $(git config user.name) <$(git config user.email)>" \
+ --in-place "$1"
+EOF
+$ chmod +x .git/hooks/prepare-commit-msg
+```
+
## Update your repo with changes in the lowRISC repo
There is a little work to do to keep everything in sync. Normally you
