docs/manual: allow sponsor mention in author name

Unfortunately not all mail providers deliver mails with subaddressing,
mention people can acknowledge a sponsor in the author name instead.

Signed-off-by: Fiona Klute (WIWA) <fiona.klute@gmx.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

docs/manual/contribute.adoc

@@ -264,6 +264,10 @@ separated from it by a plus `+` sign. E.g.:
 +
 `Your-Name Your-Surname <your-name.your-surname+their-name.their-surname@mail.com>`
 
+Alternatively, especially if your email server does not support
+subaddressing, you can include the sponsor in your author name in
+parentheses, e.g. "Your Name (Sponsor Name)".
+
 When adding new packages, you should submit every package in a
 separate patch. This patch should have the update to
 +package/Config.in+, the package +Config.in+ file, the +.mk+ file, the