wakatime: init at 6.0.1

To hack together a working WakaTime under emacs on NixOS:

* Install both `wakatime` and `(emacsWithPackages [ wakatime-mode ])`
* Add the following to your initialisation file (default: ~/.emacs):
  (custom-set-variables
   ;; ...
   '(wakatime-api-key "XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX")
   '(wakatime-cli-path "")					; sic
   '(wakatime-python-bin "/path/to/profile/bin/wakatime"))	; sic
* `M-x global-wakatime-mode` to test your settings.