general: contribute: notify after force push

In the "Finalizing your contribution section", add a sentence after the
force push advising the contributor to add a comment to notify the
maintainers.

Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
Acked-by: Jerome Forissier <jerome.forissier@linaro.org>
diff --git a/general/contribute.rst b/general/contribute.rst
index 54a1935..770b673 100644
--- a/general/contribute.rst
+++ b/general/contribute.rst
@@ -191,6 +191,9 @@
 
     $ git push -f <my-remote> <my-branch>
 
+Add a message in the comments field saying something like "Fixed up commits
+with tag and ready to be merged" to notify the maintainers.
+
 After completing this it is the project maintainers job to apply your patches to
 the master branch.