Add note about -a option to history file and clarify its description in the docs a bit.

Author: dhellmann

docs/en/command_ref.rst

@@ -41,7 +41,8 @@ activated after being initialized.
     mynewenv
     (mynewenv)$ 
 
-The ``-a`` option can be used to associate a project with the new environment.
+The ``-a`` option can be used to associate an existing project
+directory with the new environment.
 
 The ``-i`` option can be used to install one or more packages (by
 repeating the option) after the environment is created.

docs/en/history.rst

@@ -2,6 +2,12 @@
 Release History
 ===============
 
+dev
+
+  - Add ``-a`` option to :ref:`command-mkvirtualenv` to associate a
+    new virtualenv with an existing project directory. Contributed by
+    Mike Fogel (:bbuser:`mfogel`).
+
 2.10.1
 
   - Changed arguments to :ref:`command-mktmpenv` so it always creates