Improve usage documentation

[oryband]

I just started using gimme, and struggled for 30 minutes until I finally figured out how to properly use it. This is what I got confused with:

• That eval stuff is confusing. I would ask the user to add the following to his .bashprofile or .zshrc:

export GIMME_GO_VERSION=1.4.1
source $HOME/.gimme/envs/go$GIMME_GO_VERSION.env  # am i doing it right?

• Add an example usage below usage: e.g. go 1.4.1, go --force 1.4.1, go 1.4.1 /some/dir.
• What's with latest.env? There's no information on it. Should I use it instead? This should probably be mentioned in the --help and readme.
• Also, does this mean I can use gimme latest to fetch the latest version?
• You should probably tell the user to check all available arches in https://golang.org/dl/ when explaining about the GIMME_ARCH env var.
• It's unclear how to use GIMME_SILENT_ENV and GIMME_NO_ENV_ALIAS. I've set this in my .zshrc and then executed gimme 1.4.1 and still got go1.4.1.linux.amd64.env created in the env/ directory:

export GIMME_GO_VERSION=1.4.1
export GIMME_SILENT_ENV=
export GIMME_NO_ENV_ALIAS=
GIMME_ENV=$HOME/.gimme/envs/go$GIMME_GO_VERSION.env
if [[ -d $GIMME_ENV ]]; then source $GIMME_ENV; fi

Also, every time I source the env file I still get go version go1.4.1 linux/amd64 printed on my screen.

[tianon]

Definitely a big +1 from me if we can come up with some better documentation. This was originally designed specifically for the use-case of CI in mind, but I know a number of folks have found it useful outside of that and are using it for managing multiple installs of Go on their personal hosts too, so having better documentation for how to do that nicely makes a lot of sense IMO!

[meatballhat]

This is the extent of what's in my ~/.zshrc for gimme usage:

export GIMME_GO_VERSION='1.6.2'
eval "$(gimme)" 2>/dev/null

It could just as easily be the following, but I export GIMME_GO_VERSION so that it shows up when I'm looking at my env in logs and such:

eval "$(gimme 1.6.2)"

To that end, the docs already cover this (as they did at the time this issue was created fff834a), so I'm not sure what other docs are wanted/needed 😕. I'm certain that this confusion on my part is because I suffer from the myopia of having written the docs 😑. Halp!