Add path.scripts directory

Today this is "unofficial" as conf/scripts, but some people
want to share scripts across different nodes and so on. Because
they cannot configure it, they are forced to use dirty hacks
like symbolic links, which isnt going to work: we aren't going
to recursively scan conf/ and add permissions to all link targets
underneath it, thats crazy.

I really hate adding yet another configuration knob here, but
users resorting to using symlinks are going to be frustrated,
and do things in a more insecure way.

docs/reference/modules/scripting.asciidoc

@@ -85,10 +85,12 @@ supported scripting languages:
 To increase security, Elasticsearch does not allow you to specify scripts for
 non-sandboxed languages with a request. Instead, scripts must be placed in the
 `scripts` directory inside the configuration directory (the directory where
-elasticsearch.yml is). Scripts placed into this directory will automatically be
-picked up and be available to be used. Once a script has been placed in this
-directory, it can be referenced by name. For example, a script called
-`calculate-score.groovy` can be referenced in a request like this:
+elasticsearch.yml is). The default location of this `scripts` directory can be
+changed by setting `path.scripts` in elasticsearch.yml. Scripts placed into
+this directory will automatically be picked up and be available to be used.
+Once a script has been placed in this directory, it can be referenced by name.
+For example, a script called `calculate-score.groovy` can be referenced in a
+request like this:
 
 [source,sh]
 --------------------------------------------------