Document capabilities API basics

Add documentation for capabilities API, capabilities of the theming app

Signed-off-by: Julius Härtl <jus@bitgrid.net>

developer_manual/client_apis/OCS/index.rst

@@ -65,3 +65,64 @@ This request returns the available metadata of a user. Admin users can see the i
 		</data>
 	</ocs>
 
+
+----
+Capabilities API
+----
+
+Clients can obtain capabilities provided by the Nextcloud server and its apps via the capabilities OCS API.
+
+.. code::
+
+	GET /ocs/v1.php/cloud/capabilities
+	
+	
+	
+.. code:: xml
+
+    <?xml version="1.0"?>
+    <ocs>
+     <meta>
+      <status>ok</status>
+      <statuscode>100</statuscode>
+      <message>OK</message>
+      <totalitems></totalitems>
+      <itemsperpage></itemsperpage>
+     </meta>
+     <data>
+      <version>
+       <major>12</major>
+       <minor>0</minor>
+       <micro>0</micro>
+       <string>12.0 beta 4</string>
+       <edition></edition>
+      </version>
+      <capabilities>
+       <core>
+        <pollinterval>60</pollinterval>
+        <webdav-root>remote.php/webdav</webdav-root>
+       </core>
+      </capabilities>
+     </data>
+    </ocs>
+     
+	
+Theming capabilities
+--------------------
+
+Values of the theming app are exposed though the capabilities API, allowing client developers to adjust the look of clients to the theming of different Nextcloud instances.
+
+.. code:: xml
+
+    <theming>
+        <name>Nextcloud</name>
+        <url>https://nextcloud.com</url>
+        <slogan>A safe home for all your data</slogan>
+        <color>#0082c9</color>
+        <logo>http://cloud.example.com/index.php/apps/theming/logo?v=1</logo>
+        <background>http://cloud.example.com/index.php/apps/theming/logo?v=1</background>
+    </theming>
+
+
+The background value can either be an URL to the background image or a hex color value.
+