doc: how to search tmux's panes for a running program

docs/tmux.md

@@ -23,3 +23,20 @@ select-pane -T "title"
 ## Sharing a Window Across Sessions
 
 To share a window between two sessions: `tmux link-window -s <src-window> -t <dst-window>`
+
+
+## Find a Panes Running a Command
+find-window [-iCNrTZ] [-t target-pane] match-string
+  (alias: findw)
+  Search for a fnmatch(3) pattern or, with -r, regular expression match-string
+  in window names, titles, and visible content (but not history).  The flags
+  control matching behavior: -C matches only visible window contents, -N matches
+  only the window name and -T matches only the window title.  -i makes the search
+  ignore case. The default is -CNT.  -Z zooms the pane.
+
+  This command works only if at least one client is attached.
+
+```tmux
+CTRL+b + f
+<SEARCH STRING>
+```