doc: Recommend "make authenticate" after ./bootstrap.

* doc/contributing.texi (Building from Git): Move "make authenticate"
instructions below.

doc/contributing.texi

@@ -67,21 +67,6 @@ gpg:                using RSA key 3CE464558A84FDC69DB40CFB090B11993D9AEBB5
 @code{3CE464558A84FDC69DB40CFB090B11993D9AEBB5} (you may need to fetch
 this key from a key server, if you have not done it yet).
 
-From there on, you can authenticate all the commits included in your
-checkout by running:
-
-@example
-make authenticate
-@end example
-
-The first run takes a couple of minutes, but subsequent runs are faster.
-
-@quotation Note
-You are advised to run @command{make authenticate} after every
-@command{git pull} invocation.  This ensures you keep receiving valid
-changes to the repository
-@end quotation
-
 The easiest way to set up a development environment for Guix is, of
 course, by using Guix!  The following command starts a new shell where
 all the dependencies and appropriate environment variables are set up to
@@ -146,6 +131,21 @@ Finally, you have to invoke @code{make check} to run tests
 fails, take a look at installation instructions (@pxref{Installation})
 or send a message to the @email{guix-devel@@gnu.org, mailing list}.
 
+From there on, you can authenticate all the commits included in your
+checkout by running:
+
+@example
+make authenticate
+@end example
+
+The first run takes a couple of minutes, but subsequent runs are faster.
+
+@quotation Note
+You are advised to run @command{make authenticate} after every
+@command{git pull} invocation.  This ensures you keep receiving valid
+changes to the repository.
+@end quotation
+
 
 @node Running Guix Before It Is Installed
 @section Running Guix Before It Is Installed