docs: add example for SendString + escape sequences

closes: https://github.com/wez/wezterm/issues/253

docs/config/keys.markdown

@@ -491,6 +491,23 @@ return {
 }
 ```
 
+You can also emit escape sequences using `SendString`.  This example shows
+how to bind Alt-LeftArrow/RightArrow to the Alt-b/f, an emacs style
+keybinding for moving backwards/forwards through a word in a line editor:
+
+```lua
+local wezterm = require 'wezterm';
+
+return {
+  keys = {
+    -- Make Option-Left equivalent to Alt-b which many line editors interpret as backward-word
+    {key="LeftArrow", mods="OPT", action=wezterm.action{SendString="\x1bb"}},
+    -- Make Option-Right equivalent to Alt-f; forward-word
+    {key="RightArrow", mods="OPT", action=wezterm.action{SendString="\x1bf"}},
+  }
+}
+```
+
 ## DisableDefaultAssignment
 
 Has no special meaning of its own; this action will undo the registration