--- a/HACKING
+++ b/HACKING
@@ -53,8 +53,25 @@
 from gnulib but is kept in the Octave source archive.  It should be
 updated from the gnulib source as necssary.  The bootstrap script takes
 care of checking out a copy of gnulib, running the autotools, and
-generating the configure script.  Once the autogen.sh and bootstrap
-scripts complete successfully, you may run
+generating the configure script.
+
+If you have a copy of gnulib in some directory apart from the Octave
+source tree, then pass the name of that directory to the bootstrap
+script using the
+
+  --gnulib-srcdir=DIRNAME
+
+option (all options passed to autogen.sh are forwarded to the
+bootstrap script).  This way, you can share a single gnulib source
+tree among several projects.  Regardless of the location of the gnulib
+sources, the bootstrap script will try to update them if it appears
+that they are checked out using git.  Otherwise, it is your
+responsibility to keep the gnulib sources up to date.  They change
+frequently, so the best way to stay current is probably to use git to
+do the job.
+
+Once the autogen.sh and bootstrap scripts complete successfully, you may
+run
 
   $ ./configure
   $ make