Advertise in README that folk should post issues or discussion for support

[brews]

As in the title need to advertise in README that folk should post issues or discussion for support.

Asking questions in these places means others can search and find solutions to the problems in the future.

Community is important, mmkay?

[brews]

Discussions is actually populated now: https://github.com/ClimateImpactLab/isku/discussions