INSTALL: duplicate python requirements from Makefile

... and refer the reader to Makefile for other things that can be
tweaked.

Signed-off-by: Junio C Hamano <junkio@cox.net>

INSTALL

@@ -75,3 +75,15 @@ Issues of note:
           history graphically
 
 	- "ssh" is used to push and pull over the net
+
+	- "perl" and POSIX-compliant shells are needed to use most of
+	  the barebone Porcelainish scripts.
+
+	- "python" 2.3 or more recent; if you have 2.3, you may need
+          to build with "make WITH_OWN_SUBPROCESS_PY=YesPlease".
+
+ - Some platform specific issues are dealt with Makefile rules,
+   but depending on your specific installation, you may not
+   have all the libraries/tools needed, or you may have
+   necessary libraries at unusual locations.  Please look at the
+   top of the Makefile to see what can be adjusted for your needs.