Warn when required dependencies are missing.

[tjarvstrand]

Hi!

Thanks for this plugin, it's been working great for me!

However, I was trying to set it up on a new Macbook today and listing versions just failed with No compatible versions available (flutter ). I eventually figured out that this was because I hadn't installed jq but there was no clue at all that this was the problem.

It would be great if there was a warning when required system packages are missing (not sure if there are others apart from jq).

[buttonsrtoys]

I have a similar problem and just posted to SO, but maybe I should have posted here. This is what I posted.

I installed the Flutter asdf plugin and added flutter to my .tool-versions file:

golang 1.18.6
nodejs 18.3.0
flutter 3.3.9

But am getting errors that the plugin can't find jq:

~/.asdf/plugins/flutter/bin/install: line 25: jq: command not found
~/.asdf/plugins/flutter/bin/install: line 26: jq: command not found
~/.asdf/plugins/flutter/bin/install: line 27: [: -gt: unary operator expected 
Cannot find the download url for the version: 3.3.9

Investigating, I see that jq is bundled with the flutter plugin, so adding ~/.asdf/plugins/flutter/bin to my PATH fixes the problem.

I'm rolling this out for other devs and this extra step seems unnecessary. Am I missing something, or is adding the plugin path to the dev's PATH necessary?