Add tooltip to new branch button

app/views/projects/issues/_new_branch.html.haml

 - if current_user && can?(current_user, :push_code, @project) && @issue.can_be_worked_on?(current_user)
   .pull-right
-    = link_to namespace_project_branches_path(@project.namespace, @project, branch_name: @issue.to_branch_name, issue_iid: @issue.iid), method: :post, class: 'btn', title: @issue.to_branch_name do
+    = link_to namespace_project_branches_path(@project.namespace, @project, branch_name: @issue.to_branch_name, issue_iid: @issue.iid), method: :post, class: 'btn has-tooltip', title: @issue.to_branch_name do
       = icon('code-fork')
       New Branch