[Bug 1596438] New: Missing `fedpkg request-branch`

https://bugzilla.redhat.com/show_bug.cgi?id=1596438

Bug ID: 1596438
           Summary: Missing `fedpkg request-branch`
           Product: Fedora Documentation
           Version: devel
         Component: packager-guide
          Assignee: [e-mail]
          Reporter: [e-mail]
        QA Contact: [e-mail]
                CC: [e-mail]

Description of problem
======================

In Join_the_package_collection_maintainers, the step "Import, commit, and build
your package" is directly followed by "Update Your Branches (if desired)", and
"Submit Package as Update in Bodhi".

https://fedoraproject.org/wiki/Join_the_package_collection_maintainers?rd=Pa...

However the step "update branches" cannot succeed, since branches are not
created automatically.  Sure, this step is optional, but even opting out, the
next step about Bodhi won't be valid, because pushing master to Bodhi is not
allowed.

Easiest fix would be to add command such as `fedpkg request-branch f28`, as
I've been advised on mailing list and IRC:

https://lists.fedoraproject.org/archives/list/[e-mail]/...

One more note: to new packager, it's not clear if they should "desire" to
update/push to new branches; because new packager might not expect this (adding
new package to already released branch) to be allowed by policy.  It would be
nice to give a hint to the packager on this.