Merge branch 'improve-license-doc' into 'master'

Make it clearer that /licenses is the OS license templates endpoint

Following the discussion on https://gitlab.com/gitlab-org/gitlab-ce/commit/13804aba867d19009ca94d820aa7ec650a509f5a#note_4961954.

Corresponding EE MR: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/407

See merge request !4188

doc/api/README.md

@@ -33,7 +33,7 @@ following locations:
 - [Build triggers](build_triggers.md)
 - [Build Variables](build_variables.md)
 - [Runners](runners.md)
-- [Licenses](licenses.md)
+- [Open source license templates](licenses.md)
 ## Authentication