clarify role spec, dependencies and galaxy involvment.

fixes #10832

docsite/rst/playbooks_roles.rst

@@ -301,12 +301,8 @@ Role dependencies can also be specified as a full path, just like top level role
     dependencies:
        - { role: '/path/to/common/roles/foo', x: 1 }
 
-Role dependencies can also be installed from source control repos or tar files, using a comma separated format of path, an optional version (tag, commit, branch etc) and optional friendly role name (an attempt is made to derive a role name from the repo name or archive filename)::
+Role dependencies can also be installed from source control repos or tar files (via `galaxy`) using comma separated format of path, an optional version (tag, commit, branch etc) and optional friendly role name (an attempt is made to derive a role name from the repo name or archive filename). Both through the command line or via a requirements.yml passed to ansible-galaxy.
 
-    ---
-    dependencies:
-      - { role: 'git+http://git.example.com/repos/role-foo,v1.1,foo' }
-      - { role: '/path/to/tar/file.tgz,,friendly-name' }
 
 Roles dependencies are always executed before the role that includes them, and are recursive. By default, 
 roles can also only be added as a dependency once - if another role also lists it as a dependency it will