Add section on upstreaming for e-mail based workflows

Mention how we should use --from to keep original git author attribution
in place.

Signed-off-by: Stefan Schmidt <stefan.schmidt@huawei.com>

documentation/source/readme/Contribution Process.rst

@@ -196,3 +196,16 @@ For details, visit https://docs.gitlab.com/ee/development/code_review.html#code-
 Related topic: `FAQs <https://git.ostc-eu.org/docs/developer-guide/-/blob/master/documentation/source/readme/FAQs.rst>`_
 
 
+Upstreaming Patches via e-mail
+==============================
+
+When upstreaming work we have done to a project which uses an e-mail based workflow there might be some pitfalls along the way.
+Our attribution should be in place (namingly the use of the company e-mail address as git author and maybe the signed-off-by), but sending the patches via Outlook/Exchange is not possible as the server side is known to mangle the e-mail format and patches would no longer apply.
+
+As a solution we recommend subscribing your private e-mail address to the mailing list and using it for sending the patches.We assume here that you have done the git commit with your correct company e-mail address and git send-email is already configured to send out e-mails ([sendemail] section of .gitconfig).
+
+To keep the correct attribution in place we need to set set the --from field to our private e-mail when executing git send-email
+
+``$ git send-email --from my.personal.email@gmail.com --to yocto@lists.yoctoproject.org my-patch-directory/*``
+
+By doing this we can ensure that the original git author e-email address will be used when the patches are applied.