doc/org.texi (Global and local cycling): Add an online label

* doc/org.texi (Global and local cycling): Add an online label
to a reference.

Thanks to HyungSuk Ryu for reporting this.

doc/org.texi

@@ -1299,7 +1299,7 @@ Expose all direct children of the subtree.  With a numeric prefix argument N,
 expose all children down to level N@.
 @orgcmd{C-c C-x b,org-tree-to-indirect-buffer}
 Show the current subtree in an indirect buffer@footnote{The indirect buffer
-(@pxref{Indirect Buffers,,,emacs,GNU Emacs Manual}) will contain the entire
+(@pxref{Indirect Buffers,https://www.gnu.org/software/emacs/manual/html_node/emacs/Indirect-Buffers.html,,emacs,GNU Emacs Manual}) will contain the entire
 buffer, but will be narrowed to the current tree.  Editing the indirect
 buffer will also change the original buffer, but without affecting visibility
 in that buffer.}.  With a numeric prefix argument N, go up to level N and