Fix inconsistencies in `org-occur' binding

* doc/org.texi (Sparse trees): Add C-c / / binding for `org-occur'.
* lisp/org.el (org-sparse-tree): Mention "r" suffix for consistency with
  other entries in the help menu.

doc/org.texi

@@ -1565,7 +1565,7 @@ commands can be accessed through a dispatcher:
 @table @asis
 @orgcmd{C-c /,org-sparse-tree}
 This prompts for an extra key to select a sparse-tree creating command.
-@orgcmd{C-c / r,org-occur}
+@orgcmdkkc{C-c / r,C-c / /,org-occur}
 @vindex org-remove-highlights-with-change
 Prompts for a regexp and shows a sparse tree with all matches.  If
 the match is in a headline, the headline is made visible.  If the match is in

lisp/org.el

@@ -13907,7 +13907,7 @@ D      Show deadlines and scheduled items between a date range."
   (interactive "P")
   (setq type (or type org-sparse-tree-default-date-type))
   (setq org-ts-type type)
-  (message "Sparse tree: [/]regexp [t]odo [T]odo-kwd [m]atch [p]roperty
+  (message "Sparse tree: [r]egexp [t]odo [T]odo-kwd [m]atch [p]roperty
              \[d]eadlines [b]efore-date [a]fter-date [D]ates range
              \[c]ycle through date types: %s"
 	   (cl-case type