doc: Running Guix Before It Is Installed: mention ./bootstrap

* doc/contributing.texi (Running Guix Before It Is Installed): Instruct
user to run ./bootstrap before ./configure.

Signed-off-by: Jakub Kądziołka <kuba@kadziolka.net>

doc/contributing.texi

@@ -166,14 +166,15 @@ actually installing them.  So that you can distinguish between your
 ``end-user'' hat and your ``motley'' costume.
 
 To that end, all the command-line tools can be used even if you have not
-run @code{make install}.  To do that, you first need to have an environment
-with all the dependencies available (@pxref{Building from Git}), and then
-simply prefix each command with
-@command{./pre-inst-env} (the @file{pre-inst-env} script lives in the
-top build tree of Guix; it is generated by @command{./configure}).
-As an example, here is how you would build the @code{hello} package as
-defined in your working tree (this assumes @command{guix-daemon} is
-already running on your system; it's OK if it's a different version):
+run @code{make install}.  To do that, you first need to have an
+environment with all the dependencies available (@pxref{Building from
+Git}), and then simply prefix each command with @command{./pre-inst-env}
+(the @file{pre-inst-env} script lives in the top build tree of Guix; it
+is generated by running @command{./bootstrap} followed by
+@command{./configure}).  As an example, here is how you would build the
+@code{hello} package as defined in your working tree (this assumes
+@command{guix-daemon} is already running on your system; it's OK if it's
+a different version):
 
 @example
 $ ./pre-inst-env guix build hello