Go Caveats

I don’t particularly love that this isn’t the cleanest set of warnings in the world, but the combination of Homebrew, zsh & Go seems to really screw up the setting of the GOPATH & the $PATH as recommended. (*The problem seems to replicate across any non-default shell*). I’ve chucked in a few lines consequently about how to handle non-default shells.

I’ll respect if this somewhat cumbersome explanation is rejected, but hopefully it’s useful to include.
I tried both Fish & zsh and failed on both of them. It's pretty easy to reproduce.

```
➜  ~  export GOPATH=$HOME/test
➜  ~  echo $GOPATH
/Users/Bob/test
➜  ~
```
Close Terminal & Re-Open:

```
➜  ~  echo $GOPATH
(Blank Response here)
```
It's the same with setting $PATH inside Fish or zsh. Unless you either use the global path in /etc/paths or set the $PATH in ``` .zshrc ``` or ``` config.fish ``` the $PATH will self-erase the next time you open up a new terminal window/tab.

The problem is that both [fish](https://github.com/fish-shell/fish-shell/issues/527) & [zsh read](http://linuxg.net/how-to-set-a-new-path-in-bash-ksh-and-zsh/) from their own config files for such things, so unless you set the variable permanently in that shells config it won't sustain throughout new tabs/windows/etc.