manual: Mention org-agenda-set-effort

* doc/org-manual.org (Remote editing): Add entry for
org-agenda-set-effort.

Reported-by: Ian Garmaise <ian.g@phorixsol.com>
Ref: https://orgmode.org/list/CALWEx6WuTe_b2c-em8jTzx5k=XHGy1L=87tn5Ge9g3oHPp1fVA@mail.gmail.com

doc/org-manual.org

@@ -9881,6 +9881,13 @@ the other commands, point needs to be in the desired line.
   #+findex: org-agenda-priority-down
   Decrease the priority of the current item.
 
+- {{{kbd(C-c C-x e)}}} or short {{{kbd(e)}}} (~org-agenda-set-effort~) ::
+
+  #+kindex: e
+  #+kindex: C-c C-x e
+  #+findex: org-agenda-set-effort
+  Set the effort property for the current item.
+
 - {{{kbd(C-c C-z)}}} or short {{{kbd(z)}}} (~org-agenda-add-note~) ::
 
   #+kindex: z