docs(guide/controller): fix wording in list of 'Do not use'

Wording has been changed in two of the examples to read naturally.
For example:

From: 'Do not use controllers for to run stateless or stateful code
shared across controllers'

To: 'Do not use controllers for sharing stateless or stateful code
across controllers'

Closes #3454

Author: Nitrodist

docs/content/guide/dev_guide.mvc.understanding_controller.ngdoc

@@ -75,10 +75,9 @@ you have to perform your own manual DOM manipulation, encapsulate the presentati
 {@link guide/directive directives}.
 - Input formatting — Use {@link forms angular form controls} instead.
 - Output filtering — Use {@link dev_guide.templates.filters angular filters} instead.
-- To run stateless or stateful code shared across controllers — Use {@link dev_guide.services angular
+- Sharing stateless or stateful code across controllers — Use {@link dev_guide.services angular
 services} instead.
-- To instantiate or manage the life-cycle of other components (for example, to create service
-instances).
+- Managing the life-cycle of other components (for example, to create service instances).
 
 
 # Associating Controllers with Angular Scope Objects