change the build-from-source instructions

[jakecoffman]

In our README we suggest doing go install github.com/dependabot/cli/cmd/dependabot@latest which is nice and convenient.

However, Go doesn't inject VCS info when built this way, so when you run dependabot --version it outputs dependabot version 0.0.0-dev and that's not very informative.

I'm wondering if we should change our build-from-source instructions to be:

git clone https://github.com/dependabot/cli.git
cd cli
go install github.com/dependabot/cli/cmd/dependabot

Or is there another option?

Related:

• cmd/go: vcs info not stamped when built listing .go files directly golang/go#51279