review the ENC documentation

 * change the section title to the long form so it is more readable
   from the table of contents (TOC), even if you don't know the
   acronym (which is still included)

 * start by more explicitely saying what we use the ENC for, not how
   it works (which we still keep)

 * try to use the active form more (e.g. "Puppet pulls elements"
   instead of "It can be used by Puppet to define elements")

 * use `code` style for variables

 * be more explicit about role::foo

 * use the more commonly use `tor-puppet.git` root instead of
   `/etc/puppet`, because the latter is not explicit, and might hint
   that users should edit it directly on the server (which is
   definitely not the case)

howto/puppet.md

@@ -1202,28 +1202,33 @@ Otherwise the style already in use in the file should be followed.
 [Flycheck]: http://flycheck.org/
 [vim-puppet]: https://github.com/rodjek/vim-puppet
 
-### ENC
-
-ENC stands for External Node Classifier. When implemented, as is the
-case here, it causes the Puppet server to request information about
-a node before its catalog is compiled.
-
-It can be used on the Puppet server to define three elements about
-nodes:
-
- * **Environment**: is the standard way to assign nodes to a
- Puppet environment. The default is `production` which is the only
- environment currently deployed.
- * **Parameters**: is a hash where each key is made available as a
- top-scope variable in a node's manifests. We use this assign a unique
- role to each node. This role is in turn used to include a `role::foo`
- class which should only consist of a set of profile classes.
- * **Classes**: is an array of class names which Puppet includes
- on the target node. We are currently transitioning from this method
- of including classes on nodes (previously in Hiera) to the `role`
- parameter and unique role classes.
-
-These elements are defined in `/etc/puppet/hiera-enc/nodes/$fqdn.yaml`.
+### External Node Classifier (ENC)
+
+We use an External Node Classifier (or ENC for short) to classify
+nodes in different roles but also assign them environments and other
+variables. The way the ENC works is that the Puppet server requests
+information from the ENC about a node before compiling its catalog.
+
+The Puppet server pulls three elements about nodes from the ENC:
+
+ * `environment` is the standard way to assign nodes to a Puppet
+   environment. The default is `production` which is the only
+   environment currently deployed.
+
+ * `parameters` is a hash where each key is made available as a
+   top-scope variable in a node's manifests. We use this assign a
+   unique "role" to each node. The way this works is, for a given role
+   `foo`, a class `role::foo` will be included. That class should only
+   consist of a set of profile classes.
+
+ * `classes` is an array of class names which Puppet includes on the
+   target node. We are currently transitioning from this method of
+   including classes on nodes (previously in Hiera) to the `role`
+   parameter and unique role classes.
+
+For a given node named `$fqdn`, these elements are defined in
+`tor-puppet.git/hiera-enc/nodes/$fqdn.yaml`. Defaults can also be set
+in `tor-puppet.git/hiera-enc/nodes/default.yaml`.
 
 #### Role classes