Augment info about Debian package

Signed-off-by: martin f. krafft <madduck@madduck.net>
diff --git a/doc/source/install.rst b/doc/source/install.rst
index 2085117..ce3e440 100644
--- a/doc/source/install.rst
+++ b/doc/source/install.rst
@@ -7,7 +7,7 @@
 |reclass| has been `packaged for Debian`_. To use it, just install it with
 APT::
 
-  $ apt-get install reclass
+  $ apt-get install reclass [reclass-doc]
 
 .. _packaged for Debian: http://packages.debian.org/search?keywords=reclass