added tmux-keybtest in Configuration (#123)

Check what keys tmux can detect from the terminal being used.

README.md

@@ -36,6 +36,7 @@ List of helpful tmux links for various tutorials, plugins, and configuration set
 - [Guide to customizing tmux.conf](https://www.hamvocke.com/blog/a-guide-to-customizing-your-tmux-conf/)
 - [practical tmux](https://mutelight.org/practical-tmux)
 - [tmux-extra](https://github.com/brandur/tmux-extra) Configuration and scripts for sane Tmux default behavior
+- [tmux-keybtest](https://github.com/jaclu/tmux-keybtest) Check what keys tmux can detect from the terminal being used.
 - [tmux yank to system clipboard](https://www.grailbox.com/2020/08/use-system-clipboard-for-vi-copy-mode-in-tmux-in-macos-and-linux/) A way to get the System Clipboard to work with tmux yank on a Mac via `pbcopy` and linux via `xclip`
 
 ## <a name="tools"></a>Tools and session management