tip: edit .asd files as lisp files

[vindarel]

Tip for using [#Pulsar](https://framapiaf.org/tags/Pulsar) IDE with [#CommonLisp](https://framapiaf.org/tags/CommonLisp): 
Edit your .asd files as lisp files by adding the following snippet to your config.cson:

  core:
    customFileTypes:
      'source.lisp': [
        'asd'
      ]

from thezerobyte on Mastodon (https://anticapitalist.party/@thezerobit/116233873351051560)

[neil-lindquist]

Thanks for the suggestion, I just added it to the README.