Update plugin doc

doc/plugin-ldap-client.markdown

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+LDAP Library
+============
+
+To facilitate LDAP integrations, Kanboard have its own LDAP library.
+This library can perform common operations.
+
+Client
+------
+
+Class: `Kanboard\Core\Ldap\Client`
+
+To connect to your LDAP server easily, use this method:
+
+```php
+use Kanboard\Core\Ldap\Client as LdapClient;
+use Kanboard\Core\Ldap\ClientException as LdapException;
+
+try {
+    $client = LdapClient::connect();
+
+    // Get native LDAP resource
+    $resource = $client->getConnection();
+
+    // ...
+
+} catch (LdapException $e) {
+    // ...
+}
+```
+
+LDAP Queries
+------------
+
+Classes:
+
+- `Kanboard\Core\Ldap\Query`
+- `Kanboard\Core\Ldap\Entries`
+- `Kanboard\Core\Ldap\Entry`
+
+Example to query the LDAP directory:
+
+```php
+
+$query = new Query($client)
+$query->execute('ou=People,dc=kanboard,dc=local', 'uid=my_user', array('cn', 'mail'));
+
+if ($query->hasResult()) {
+    $entries = $query->getEntries(); // Return an instance of Entries
+}
+```
+
+Read one entry:
+
+```php
+$firstEntry = $query->getEntries()->getFirstEntry();
+$email = $firstEntry->getFirstValue('mail');
+$name = $firstEntry->getFirstValue('cn', 'Default Name');
+```
+
+Read multiple entries:
+
+```php
+foreach ($query->getEntries()->getAll() as $entry) {
+    $emails = $entry->getAll('mail'); // Fetch all emails
+    $dn = $entry->getDn(); // Get LDAP DN of this user
+
+    // Check if a value is present for an attribute
+    if ($entry->hasValue('mail', 'user2@localhost')) {
+        // ...
+    }
+}
+```
+
+User Helper
+-----------
+
+Class: `Kanboard\Core\Ldap\User`
+
+Fetch a single user in one line:
+
+```php
+// Return an instance of LdapUserProvider
+$user = User::getUser($client, 'my_username');
+```
+
+Group Helper
+------------
+
+Class: `Kanboard\Core\Ldap\Group`
+
+Fetch groups in one line:
+
+```php
+// Define LDAP filter
+$filter = '(&(objectClass=group)(sAMAccountName=My group*))';
+
+// Return a list of LdapGroupProvider
+$groups = Group::getGroups($client, $filter);
+```