Merge branch '21451-change-merge-request-text-after-pushing-new-branch' into 'master'

Make merge request text after push clearer

The message to create a merge request after pushing a new branch was not clear. It is now clear that it is optional to create a merge request for the pushed branch.

Part of [#21451](https://gitlab.com/gitlab-org/gitlab-ce/issues/21451)

See merge request !109