winsup/doc: Update ancient README about building documentation

Update list of pre-requisites, everything else is obsolete.

Future work: Ensure that the list of pre-requisites in FAQ 6.21 "How do I build
Cygwin" remains synchronized with this list.

2015-06-22  Jon Turney  <jon.turney@dronecode.org.uk>

	* README: Update.

Signed-off-by: Jon TURNEY <jon.turney@dronecode.org.uk>

winsup/doc/ChangeLog

@@ -1,3 +1,7 @@
+2015-06-22  Jon Turney  <jon.turney@dronecode.org.uk>
+
+	* README: Update.
+
 2015-06-22  Jon Turney  <jon.turney@dronecode.org.uk>
 
 	* Makefile.in (FAQ_SOURCES): Remove and generate with xidepend.

winsup/doc/README

@@ -1,28 +1,9 @@
-The cygwin-doc source files are kept in CVS. Please see
+ADDITIONAL BUILD REQUIREMENTS FOR DOCUMENTATION
-https://cygwin.com/cvs.html for more information.
 
-BUILD REQUIREMENTS:
-
-bash
-bzip2
-coreutils
-cygwin
 dblatex
 docbook-xml45
 docbook-xsl
+docbook2x-texi
 gzip
-make
 texinfo
-perl
 xmlto
-
-OTHER NOTES:
-
-You may use docbook2X to convert the DocBook files into info pages.
-I have not been able to get a working docbook2X installation on Cygwin,
-so currently I convert the files on a machine running GNU/Linux.
-
-A few handmade files (cygwin.texi, intro.3, etc.) are found in the
-cygwin-doc-x.y-z-src.tar.bz2 package. It also contains the utilities for
-building the cygwin-doc-x.y-z "binary" package--simply run each step in
-the cygwin-doc-x.y-z.sh script.