INSTALL: document a simpler way to run uninstalled builds

The new scripts automatically saved in the bin-wrappers directory allow
you to run a build when you have neither installed git nor tweaked
environment variables.  Mention this in INSTALL, along with the slight
performance issue of doing so.

This can be especially handy for manually testing network-invoked git
(from ssh, web servers, or similar), but it is also handy with a plain
command prompt.
Signed-off-by: NMatthew Ogilvie <mmogilvi_git@miniinfo.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

INSTALL

@@ -38,13 +38,17 @@ Issues of note:
    Interactive Tools package still can install "git", but you can build it
    with --disable-transition option to avoid this.
 
- - You can use git after building but without installing if you
-   wanted to.  Various git commands need to find other git
-   commands and scripts to do their work, so you would need to
-   arrange a few environment variables to tell them that their
-   friends will be found in your built source area instead of at
-   their standard installation area.  Something like this works
-   for me:
+ - You can use git after building but without installing if you want
+   to test drive it.  Simply run git found in bin-wrappers directory
+   in the build directory, or prepend that directory to your $PATH.
+   This however is less efficient than running an installed git, as
+   you always need an extra fork+exec to run any git subcommand.
+
+   It is still possible to use git without installing by setting a few
+   environment variables, which was the way this was done
+   traditionally.  But using git found in bin-wrappers directory in
+   the build directory is far simpler.  As a historical reference, the
+   old way went like this:
 
 	GIT_EXEC_PATH=`pwd`
 	PATH=`pwd`:$PATH