[docgen] Update doc/orgmode.txt

Author: github-actions

doc/orgmode.txt

@@ -568,7 +568,7 @@ Variables:
   * `%x`: Insert content of the clipboard via the "+" register (see :help clipboard)
   * `%?`: Default cursor position when template is opened
   * `%^{PROMPT|DEFAULT|COMPLETION...}`: Prompt for input, if completion is provided an :h inputlist will be used
-  * `%(EXP)`: Runs the given lua code and inserts the result
+  * `%(EXP)`: Runs the given lua code and inserts the result. NOTE: this will internally pass the content to the lua `load()` function. So the body inside `%()` should be the body of a function that returns a string.
 
 Example:
 >
@@ -607,6 +607,16 @@ Nested key example:
       }
 <
 
+Lua expression example:
+>
+      { j = {
+        description = 'Journal',
+        template = '* %(return vim.fn.getreg "w")',
+        -- get the content of register "w"
+        target = '~/sync/org/journal.org'
+      } }
+<
+
 ORG_AGENDA_MIN_HEIGHT                              *orgmode-org_agenda_min_height*
 
 type: `number`