Added better help description to the size limit fields.

app/helpers/groups_helper.rb

@@ -44,7 +44,7 @@ module GroupsHelper
   def size_limit_message_for_group(group)
     show_lfs = group.lfs_enabled? ? 'and their respective LFS files' : ''
 
-    "Repositories within this group #{show_lfs} will be restricted to this maximum size. Can be overridden inside each project. 0 for unlimited."
+    "Repositories within this group #{show_lfs} will be restricted to this maximum size. Can be overridden inside each project. 0 for unlimited. Leave empty to inherit the global value."
   end
 
   def group_lfs_status(group)

app/helpers/projects_helper.rb

@@ -217,7 +217,7 @@ module ProjectsHelper
   def size_limit_message(project)
     show_lfs = project.lfs_enabled? ? 'including files in LFS' : ''
 
-    "The total size of this project's repository #{show_lfs} will be limited to this size. 0 for unlimited."
+    "The total size of this project's repository #{show_lfs} will be limited to this size. 0 for unlimited. Leave empty to inherit the group/global value."
   end
 
   def git_user_name