add missing docstring for functions

The '?' key bindings uses them for the help window and these are
currently empty.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

emacs/notmuch-hello.el

@@ -249,6 +249,7 @@ should be. Returns a cons cell `(tags-per-line width)'."
   (notmuch-hello-update t))
 
 (defun notmuch-hello-update (&optional no-display)
+  "Update the current notmuch view."
   ;; Lazy - rebuild everything.
   (interactive)
   (notmuch-hello no-display))

emacs/notmuch-mua.el

@@ -118,6 +118,7 @@ list."
 
 (defun notmuch-mua-mail (&optional to subject other-headers continue
 				   switch-function yank-action send-actions)
+  "Invoke the notmuch mail composition window."
   (interactive)
 
   (when notmuch-mua-user-agent-function