docs: pub activate issue and restricted docs

[HayesGordon]

Awesome package and can't wait to play around with it.

The doc mentioned in the readme is giving a 404: https://github.com/wolfenrain/umbra/tree/main/docs

And running dart pub global activate umbra_cli

Gives:

dart pub global activate umbra_cli
Because pub global activate depends on umbra_cli any which doesn't exist
  (could not find package umbra_cli at https://pub.dartlang.org), version
  solving failed

[wolfenrain]

Hi both of those are correct, as I havent yet published the CLI nor written the documentation!

Planning on doing the docs in my next PR, had to make the API less opinionated.

If you want to play around with it already you can clone it locally and run dart pub global activate --source path . inside packages/umbra_cli to get the CLI installed.

[HayesGordon]

Already did that and played around! This is a really nice initiative, thanks for the work.

[wolfenrain]

I just released the first dev version! So closing this issue ;-).