docs: update Explanation index and landing page

Author: tmihoc

explanation/cli_tools.md

@@ -1,3 +1,4 @@
+(juju-vs-jaas-vs-jimmctl)=
 # `juju` vs. `jaas` vs. `jimmctl`
 
 This document aims to explain the differences between the various CLI tools you may encounter when using Juju and JAAS.

explanation/index.md

@@ -5,9 +5,22 @@
 ```{toctree}
 :titlesonly:
 :glob:
+:hidden:
 
 *
 ```
+
+## JAAS at a glance
+
+- {ref}`Architecture <jaas-architecture>`
+- {ref}`Authentication <jaas-authentication>`
+- {ref}`Authorization <jaas-authorization>`
+- {ref}`Security <jaas-security-overview>`
+
+## JAAS tooling
+
+- {ref}`juju-vs-jaas-vs-jimmctl`
+
 <!--
 An important precursor to understanding JAAS, is Juju, the open source orchestration engine for software operators.