Xnamespace: add some documentation

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>

doc/Xnamespace.md

@@ -0,0 +1,26 @@
+Xnamespace extension v1.0
+=========================
+
+This extension separates clients into several namespaces (a bit similar to
+Linux's kernel namespaces), which are isolated from each other. For example,
+namespaces have their own selections and clients cannot directly interact
+(send messages) or access other client's resources across namespace borders.
+
+An exception is the `root` namespace, which completely is unrestricted.
+
+Configuration
+-------------
+
+Namespaces are defined in a separate configuration file, which is loaded at
+server startup (no dynamic provisioning in this version yet). The extension
+is enabled when a namespace config is passed to the Xserver via the
+`-namespace <fn>` flag.
+
+
+See `Xext/namespace/ns.conf.example` for a configuration file example.
+
+Authentication / Namespace assignment
+-------------------------------------
+
+Assignment of clients into namespaces is done by the authentication token the
+client is using to authenticate. Thus, token authentication needs to enabled.