docs/manual: update graph-depends documentation about --stop-on

This commit updates the graph-depends documentation to take into
account the new 'host' keyword that can be passed to the --stop-on and
--exclude options.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

docs/manual/common-usage.txt

@@ -212,9 +212,10 @@ The +graph-depends+ behaviour can be controlled by setting options in the
   default, +0+, means no limit.
 
 * +--stop-on PKG+, +-s PKG+, to stop the graph on the package +PKG+.
-  +PKG+ can be an actual package name, a glob, or the keyword 'virtual'
-  (to stop on virtual packages). The package is still present on the
-  graph, but its dependencies are not.
+  +PKG+ can be an actual package name, a glob, the keyword 'virtual'
+  (to stop on virtual packages), or the keyword 'host' (to stop on
+  host packages). The package is still present on the graph, but its
+  dependencies are not.
 
 * +--exclude PKG+, +-x PKG+, like +--stop-on+, but also omits +PKG+ from
   the graph.