[PATCH] update templates doc to better explain the default style

[Haszlakiewicz, Eric]

Here's a slight clarification to how the --style option works, and a pointer to the most up to date info (since this ends up in relatively static hg.1 man page):

diff --git a/mercurial/help/templates.txt b/mercurial/help/templates.txt
--- mercurial/help/templates.txt
+++ mercurial/help/templates.txt
@@ -13,6 +13,15 @@
 
     $ hg log -r1 --style changelog
 
+The --style option can specify an explicit filename, or the name of
+a pre-installed style.  The pre-installed styles are located in
+<install-dir>/lib/python<version>/site-packages/mercurial/templates/map-cmdline.<style>
+
+However, for performance reasons the map-cmdline.default style file is only
+present for reference, as a compiled in default is used when --style is not
+specified.  You can force the non-compiled-in default to be used by specifying
+--style default.
+
 A template is a piece of text, with markup to invoke variable
 expansion::
 
@@ -22,6 +31,7 @@
 Strings in curly braces are called keywords. The availability of
 keywords depends on the exact context of the templater. These
 keywords are usually available for templating a log-like command:
+(See the output of "hg help templates" for a more up-to-date list.)
 
 .. keywordsmarker
 
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