Update README for Go installation

[akostibas]

Description

Updating the README to be in line with how installing Go from brew works.

Brew seems to have removed the ability to install specific go versions:

$ brew install go@1.11.5
Error: No available formula with the name "go@1.11.5" 
==> Searching for a previously deleted formula (in the last month)...
Warning: homebrew/core is shallow clone. To get complete history run:
  git -C "$(brew --repo homebrew/core)" fetch --unshallow

Error: No previously deleted formula found.
==> Searching for similarly named formulae...
Error: No similarly named formulae found.
==> Searching taps...
==> Searching taps on GitHub...
Error: No formulae found in taps.

Thus, the best we can do right now is install the latest version and pin it.
[EDIT: actually, the only versions it provides are minor versions, such as go@1.9, go@1.8, etc. Which leaves us in the same place.]

I did look into using goenv (https://github.com/syndbg/goenv) which seems like a nice alternative. However, the version of goenv in brew doesn't support installing go1.11.5... so, 🔥.

[mikena-truss]

Thanks!

[chrisgilmerproj]

This is a much better way to handle this. I didn't even know about brew pin and brew unpin!

I might still suggest that you mention to people that previously set their $PATH that it be either removed or changed to export PATH="/usr/local/opt/go/bin:$PATH".

[chrisgilmerproj]

👍

[chrisgilmerproj]

👍