[wwwdocs] Add a README for htdocs/install

[Gerald Pfeifer]

In http://gcc.gnu.org/PR54711 Steve  wrote the following:

  OK, I can check out wwwdocs but the page I am interested in doesn't seem 
  to be there.  On the web it is http://gcc.gnu.org/install/test.html, but 
  I can't seem to find this page in a checked out version of wwwdocs.  I 
  did get an htdocs/install directory but it does not include any files 
  (other than CVS and .cvsignore).

Looking at our web tree, I can totally see how this can be confusing,
and I hope the patch below that adds a new htdocs/install/README file
helps avoid this going forward.

Applied.

Steve, if you have a suggestion for some different or additional wording,
based on your experience, please advise.

Gerald

Index: README
===================================================================
RCS file: README
diff -N README
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ README	29 Dec 2012 00:43:46 -0000
@@ -0,0 +1,3 @@
+The contents of this directory is not actually maintained here, but
+created from gcc/doc/install.texi and regularily synced from the GCC
+source tree to gcc.gnu.org.