Add formatting to GitLab dev permissions guide

doc/development/permissions.md

@@ -9,9 +9,9 @@ anything that deals with permissions, all of them should be considered.
 
 Groups and projects can have the following visibility levels:
 
-- public (20) - an entity is visible to everyone
-- internal (10) - an entity is visible to logged in users
-- private (0) - an entity is visible only to the approved members of the entity
+- public (`20`) - an entity is visible to everyone
+- internal (`10`) - an entity is visible to logged in users
+- private (`0`) - an entity is visible only to the approved members of the entity
 
 The visibility level of a group can be changed only if all subgroups and
 subprojects have the same or lower visibility level. (e.g., a group can be set