(docs) Add new documentation file to leftnav

Author: austb

documentation/_puppetdb_nav.html

@@ -20,6 +20,7 @@ <h2 id="puppetdb">PuppetDB {{ page.doc.my_versions.puppetdb }}</h2>
 * **Configuration**
     * [Configuring PuppetDB]({{puppetdb}}/configure.html)
     * [puppetdb.conf: Configuring a Puppet/PuppetDB connection]({{puppetdb}}/puppetdb_connection.html)
+    * [Configuring Postgres]({{puppetdb}}/configure_postgres.html)
     * [Setting up SSL for PostgreSQL]({{puppetdb}}/postgres_ssl.html)
 * **Usage/admin**
     * [Using PuppetDB]({{puppetdb}}/using.html)

documentation/configure_postgres.markdown

@@ -53,9 +53,10 @@ Particularly if you plan to run more than one PuppetDB instance
 connecting to the same database, we recommend you also
 [add and use a "migrator" user](#coordinating-database-migrations)
 
-You should install the RegExp-optimized index extension
-[`pg_trgm`][pg_trgm]. This may require installing the
-`postgresql-contrib` (or equivalent) package, depending on your
+Install the [`pg_trgm`][pg_trgm] extension. PuppetDB makes use of this
+extension to improve the performance of queries that use regular expression
+filters (e.g. `certname ~ "abc\d+.example.com"`). This may require installing
+the `postgresql-contrib` (or equivalent) package, depending on your
 distribution:
 
     $ sudo -u postgres sh

documentation/puppetdb.ditamap

@@ -32,6 +32,7 @@
     <topichead navtitle="Configuration">
       <topicref href="configure.markdown" format="markdown"/>
       <topicref href="puppetdb_connection.markdown" format="markdown"/>
+      <topicref href="configure_postgres.markdown" format="markdown"/>
       <topicref href="postgres_ssl.markdown" format="markdown"/>
     </topichead>