added missing keybinding to README.md

CHANGELOG.md

@@ -7,3 +7,7 @@ and this project adheres to the
 [Haskell Package Versioning Policy](https://pvp.haskell.org/).
 
 ## [Unreleased]
+
+### Fixed
+
+- missing keybinding in README.md

README.md

@@ -38,6 +38,7 @@ command line.  There are currently no command-line options.
 - down/j: move the rung selector down
 - PgUp/K/S-up: select the top rung
 - PgDn/J/S-down: select the bottom rung
+- 0..9: select a rung by number
 - left/h: slide a bead to the left
 - right/l: slide a bead to the right
 - Home/H/S-left: move the entire rung to the left