Merge branch 'ff-rebase-docs' into 'master'

ff-rebase-docs

See merge request gitlab-org/gitlab-ee!3137

doc/user/project/merge_requests/fast_forward_merge.md

@@ -9,7 +9,7 @@ When the fast-forward merge ([`--ff-only`][ffonly]) setting is enabled, no merge
 commits will be created and all merges are fast-forwarded, which means that
 merging is only allowed if the branch could be fast-forwarded.
 
-When a fast-forward merge is not possible, the user must rebase the branch manually.
+When a fast-forward merge is not possible, the user is given the option to rebase.
 
 ## Use cases
 
@@ -25,7 +25,7 @@ merge commits. In such cases, the fast-forward merge is the perfect candidate.
 Now, when you visit the merge request page, you will be able to accept it
 **only if a fast-forward merge is possible**.
 
-![Fast forward merge request](img/ff_merge_mr.png)
+![Fast forward merge request](img/ff_merge_rebase.png)
 
 If the target branch is ahead of the source branch, you need to rebase the
 source branch locally before you will be able to do a fast-forward merge.