support/gnuconfig: update README.buildroot with reality

4 out of 5 packages who are not using autotools but needed their
gnuconfig files updated were not complying with the recommandation in
support/gnuconfig/README.buildroot. The fifth package was converted to
be like the others: use UPDATE_CONFIG_HOOK as a <pkg>_POST_PATCH_HOOKS
rather than calling the CONFIG_UPDATE macro directly.

Now that all packages are consistent, update the README.buildroot file
to match the reality.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

support/gnuconfig/README.buildroot

@@ -10,7 +10,7 @@ If for some reason your package does not use the autotools-package
 infrastructure, you can request the config.guess and/or config.sub
 files of your package to be updated by using:
 
-      $(call CONFIG_UPDATE,directory-of-your-package-sources)
+<pkg>_POST_PATCH_HOOKS += UPDATE_CONFIG_HOOK
 
 --- UPDATE ---
 GNU config is now managed in git, so to update: