feat(devmanual): Document contacts menu basics

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

developer_manual/digging_deeper/groupware/contacts_menu.rst

@@ -0,0 +1,89 @@
+=============
+Contacts Menu
+=============
+
+Nextcloud shows a *Contacts menu* in the right corner of the header. This menu lists a user's contacts. These contact entries can be extended by apps.
+
+Apps that extend the contacts menu implement an IProvider. The providers ``process`` method is called for every entry show in the contacts menu.
+
+.. code-block:: php
+    :caption: lib/ContactsMenu/MyProvider.php
+
+    <?php
+
+    namespace OCA\MyApp\ContactsMenu;
+
+    use OCP\Contacts\ContactsMenu\IEntry;
+    use OCP\Contacts\ContactsMenu\IProvider;
+
+    class MyProvider implements IProvider {
+        public function process(IEntry $entry): void {
+            // todo: something useful
+        }
+    }
+
+
+.. code-block:: xml
+    :caption: appinfo/info.xml
+    :emphasize-lines: 6-8
+
+    <?xml version="1.0"?>
+    <info xmlns:xsi= "http://www.w3.org/2001/XMLSchema-instance"
+        xsi:noNamespaceSchemaLocation="https://apps.nextcloud.com/schema/apps/info.xsd">
+        <id>my_app</id>
+        <name>My App</name>
+        <contactsmenu>
+            <provider>OCA\MyApp\ContactsMenu\LinkActionProvider</provider>
+        </contactsmenu>
+    </info>
+
+Accessing contact info
+^^^^^^^^^^^^^^^^^^^^^^
+
+The ``IEntry`` objects offer getters to contact infos:
+
+* ``getFullName()``: Get full name. Falls back to an empty string if no full name is set.
+* ``getEMailAddresses()``: Get all email addresses.
+* ``getAvatar()``: Get the avatar URI.
+* ``getProperty(string $name)``: Read a property of the contact. Return NULL if the property is not set.
+
+Actions
+^^^^^^^
+
+Providers can add actions to contact entries. Right now email and link actions are supported. These are created with the help of the ``IActionFactory``.
+
+.. code-block:: php
+    :caption: lib/ContactsMenu/LinkProvider.php
+
+    <?php
+
+    namespace OCA\MyApp\ContactsMenu;
+
+    use OCP\Contacts\ContactsMenu\IEntry;
+    use OCP\Contacts\ContactsMenu\IProvider;
+
+    class LinkProvider implements IProvider {
+        private IActionFactory $actionFactory;
+
+        public function __construct(IActionFactory $actionFactory) {
+            $this->actionFactory = $actionFactory
+        }
+
+        public function process(IEntry $entry): void {
+            $emailAction = $this->actionFactory->newEMailAction(
+                '/apps/myapp/img/link.png', // icon URL
+                'Click me', // name
+                'user@domain.tld', // email address
+                'my_app', // app ID (optional)
+            );
+            $linkAction = $this->actionFactory->newLinkAction(
+                '/apps/myapp/img/link.png', // icon URL
+                'Click me', // name
+                'https://.....', // href
+                'my_app', // app ID (optional)
+            );
+
+            $entry->addAction($emailAction);
+            $entry->addAction($linkAction);
+        }
+    }

developer_manual/digging_deeper/groupware/index.rst

@@ -7,3 +7,4 @@ Groupware integration
 
    calendar
    calendar_provider
+   contacts_menu