Add new auth doc to documentation index.

www/pages/documentation.md

@@ -26,8 +26,9 @@
 
 # Other
 
-* [Using the snap package] - specific instructions on installing and configuring the Mosquitto snap package.
+* [Authentication methods] - details on the different authentication options available.
 * [Dynamic Security plugin] - details of using the Dynamic Security authentication and access control plugin.
+* [Using the snap package] - specific instructions on installing and configuring the Mosquitto snap package.
 * [Migrating from 1.x to 2.0] - details of changes needed to migrate to version 2.0.
 
 [mosquitto]:/man/mosquitto-8.html
@@ -41,6 +42,7 @@
 
 [libmosquitto API documentation]:/api/
 
+[Authentication methods]:/documentation/authentication-methods/
 [Using the snap package]:/documentation/using-the-snap/
 [Dynamic Security plugin]:/documentation/dynamic-security/
 [Migrating from 1.x to 2.0]:/documentation/migrating-to-2-0/