excise reference to crypto implementation from main docs

It's too scary for the uninitiated.

site/features.md

@@ -157,10 +157,7 @@ or
 _NOTE: The command line option takes precedence over the environment
 variable._
 
-The same password must be specified for all weave peers; it is a
-component in the creation of ephemeral session keys for connections
-between peers. See the [crypto documentation](how-it-works.html#crypto)
-for more details.
+The same password must be specified for all weave peers.
 
 ### <a name="host-network-integration"></a>Host network integration
 

site/systemd.md

@@ -69,4 +69,4 @@ context with the commands shown below. You will need to have the
 [readme]: https://github.com/weaveworks/weave/blob/master/README.md#installation
 [connect]: features.html#dynamic-topologies
 [systemd]: http://www.freedesktop.org/wiki/Software/systemd/
-[encryption]: how-it-works.html#crypto
+[encryption]: features.html#security