add user config api docs

mkdocs/docs/api/config.md

@@ -0,0 +1,18 @@
+# Config
+
+## User Config
+Per user modified config values.
+
+**GET** `/api/config/user/`  
+Return all config values *modified* by user.
+
+**POST** `/api/config/user/`  
+Modify one or more config values. For possible key, values, see `UserConfig` class.
+
+Example post data:
+```json
+{
+    "colors": "dark",
+    "page_size": 20
+}
+```

mkdocs/mkdocs.yml

@@ -39,6 +39,7 @@ nav:
         - 'Backup': 'api/backup.md'
         - 'Task': 'api/task.md'
         - 'Stats': 'api/stats.md'
+        - 'Config': 'api/config.md'
         - 'Additional': 'api/additional.md'
     - Links:
         - 'Main site': https://www.tubearchivist.com