workflows Clarify workflow format

Hi, at https://github.com/warpdotdev/workflows/blob/main/FORMAT.md#shells it said the shell field can be unspecified, but it can not be omitted:

...
shells: [] << this line must exist even though you don't specify single shell name.
...

shortly, "If not specified" can be interpreted in two ways: leave it as empty array or omit the field. I think it would be much helpful to point out the very first one.

Or, maybe we can provide a bolierplate workflow file which has only required fields.

Apr 20 '22 05:04 roeniss

@roeniss did i already get your discord username? If not let me know, so I can add the Contributor discord role!

Apr 23 '22 04:04 elviskahoro

Hey @roeniss! Thank you so much for filling and sorry for the confusion here. It's actually both, it can either be left unspecified or be omitted entirely.

l'll work on making this clearer, it looks like it's also not specified whether it's required or optional in our format file either: https://github.com/warpdotdev/workflows/issues/61

Apr 25 '22 14:04 alokedesai

@alokedesai Good! my discord name is Roeniss Moon#6355

Apr 29 '22 15:04 roeniss

@alokedesai I think you did this right?

Aug 03 '22 22:08 elviskahoro

Yes I believe this is done, please reopen if you feel that this is still confusing!

Sep 15 '22 00:09 alokedesai