Add docs/tests for groups api

doc/api/groups.md

@@ -0,0 +1,45 @@
+## List project groups
+
+Get a list of groups. (As user: my groups, as admin: all groups)
+
+```
+GET /groups
+```
+
+```json
+[
+    {
+        "id": 1,
+        "name": "Foobar Group",
+        "path": "foo-bar",
+        "owner_id": 18
+    }
+]
+```
+
+## Details of group
+
+Get all details of a group.
+
+```
+GET /groups/:id
+```
+
+Parameters:
+
++ `id` (required) - The ID of a group
+
+## New group
+
+Create a new project group. Available only for admin
+
+```
+POST /groups
+```
+
+Parameters:
++ `name` (required)                  - Email
++ `path`                             - Password
+
+Will return created group with status `201 Created` on success, or `404 Not found` on fail.
+