Update README for installing with Go

[macintacos]

On Go 1.17, go get -u as a method of installation locally was deprecated, and on 1.18 it completely fails to run. Switching to go install github.com/arl/gitmux@latest works as expected on 1.17+.

Purpose

To make the README slightly more accurate depending on what version you have chosen.

Approach

Clearly denotes what command to use depending on what version of Go you decide to use.

[arl]

Thanks for doing this, much appreciated!

Since we're way past 1.18 release, and soon 1.19, i'm even wondering if we should just directly give install instructions saying that we need go1.17+ and go install.
What do you think?

[macintacos]

Sounds perfectly reasonable, I can adjust. I didn't test this on anything other than Go 1.18, however (did the lookup to find that it was deprecated on 1.17). I don't know if go install works on 1.15 or 1.16. Do you have the means to test that out? Otherwise I can do it, just will take a bit for me to get around to it (this was kind-of just a fly-by PR 🙂)

I guess you could also bump go.mod to 1.17 minimum (that's probably what I would do if I were in your shoes). Let me know what you would like to do!

[arl]

go install ... has been working since go1.16 (included).
I guess it's totally fine to increase the min version from 1.15 to 1.16 in the README.

I'll take care of go.mod in another PR, i prefer this to just be about the README.
Thank you 🙏

[macintacos]

@arl ready for another look!

[arl]

Thanks a lot!