README: prefer vicious in global space

We want to expose suspend, activate and force functions to external
shell scripts not just the Lua prompt.

README

@@ -35,7 +35,7 @@ your memory.
 
 Then add the following to the top of your rc.lua:
 
-  local vicious = require("vicious")
+  vicious = require("vicious")
 
 Once you create a widget (a textbox, graph or a progressbar) call
 vicious.register() to register it with Vicious:

contrib/README

@@ -13,7 +13,7 @@ To use contrib widgets uncomment the line that loads them in
 init.lua. Or you can load them in your rc.lua after you require
 Vicious:
 
-  local vicious = require("vicious")
+  vicious = require("vicious")
   vicious.contrib = require("vicious.contrib")