Improve README with fork / PR instructions

[faermanj]

Hello,

My attempt to fork and build faild, probably a newbie mistake due to go vendoring:

go: inconsistent vendoring in /Users/julio/Dev/aws-nuke:
	golang.org/x/[email protected]: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt
	golang.org/x/[email protected]: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt

	To ignore the vendor directory, use -mod=readonly or -mod=mod.
	To sync the vendor directory, run:
		go mod vendor
make: *** [go_generate] Error 1

The suggested commands did not resolve. I could build fine from main. If you let me know how to set up a fork i would gladly contribute it to the README, and hopefully more :)

Cheers

[ekristen]

That command should definitely work if you are using go modules in your golang setup. I just forked and made changes without issue. Are you still experience issues with the latest code base @faermanj?