[PATCH] docs: mention $MAKE during configure

Based on a suggestion from Bob Friesenhahn:
https://lists.gnu.org/archive/html/bug-automake/2013-01/msg00017.html

* doc/install.texi (Defining Variables): Mention that MAKE
can be overridden, and the caveats that come with setting it.
---

How does this look?

 doc/install.texi | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/doc/install.texi b/doc/install.texi
index 4c2ffb5..bb08786 100644
--- a/doc/install.texi
+++ b/doc/install.texi
@@ -5,7 +5,7 @@

 @unnumbered Installation Instructions

-Copyright @copyright{} 1994-1996, 1999-2002, 2004-2012 Free Software
+Copyright @copyright{} 1994-1996, 1999-2002, 2004-2013 Free Software
 Foundation, Inc.

 Copying and distribution of this file, with or without modification, are
@@ -371,6 +371,14 @@ Defining Variables
 CONFIG_SHELL=/bin/bash ./configure CONFIG_SHELL=/bin/bash
 @end example

+Another variable to be aware of is @env{MAKE}; many packages allow this
+to be set during @command{configure} in order to request the use of an
+alternative @command{make} implementation (such as GNU make, which is
+often present as @command{gmake}).  However, once an alternative is
+chosen, the resulting Makefile may no longer work with the generic
+@command{make}, so you must make sure to consistently use your
+alternative make.
+
 @node configure Invocation
 @section @command{configure} Invocation

-- 
1.8.0.2