Added support for LDAP user photo profile

doc/ldap-profile-picture.markdown

@@ -0,0 +1,27 @@
+LDAP User Profile Photo
+=======================
+
+Kanboard can download automatically user pictures from the LDAP server.
+
+This feature is enabled only if LDAP authentication is activated and the parameter `LDAP_USER_ATTRIBUTE_PHOTO` is defined.
+
+Configuration
+-------------
+
+In your `config.php`, you have to set the LDAP attribute used to store the image.
+
+```php
+define('LDAP_USER_ATTRIBUTE_PHOTO', 'jpegPhoto');
+```
+
+Usually, the attributes `jpegPhoto` or `thumbnailPhoto` are used.
+The image can be stored in JPEG or PNG format.
+
+To upload the image in the user profile, Active Directory administrators may use software like [AD Photo Edit](http://www.cjwdev.co.uk/Software/ADPhotoEdit/Info.html).
+
+Notes
+-----
+
+The profile image is **downloaded at login time only if the user do not already have uploaded an image previously**.
+
+To change the user photo, the previous one have to be removed manually in the user profile.