Be more helpful when we detect a new version of the cli #597

Currently when the cli detects a newer version, we show this:

➜ wnfs-migration (issue-2) ✗ fission whoami
⚠️  A new version of Fission CLI is available: 2.17.2 (AKA 'Wicket')

At minimum, we should link to the docs on upgrading the cli:

https://guide.fission.codes/developers/installation#upgrading-the-cli

Bonus round - if we can know the method of installation ( brew vs source build vs ... ) based on some data captured on install / post-install, we could be even smarter and just display targeted instructions eg

➜ wnfs-migration (issue-2) ✗ fission whoami
⚠️  A new version of Fission CLI is available: 2.17.2 (AKA 'Wicket') - please run 'brew upgrade fission-cli'