copy binary to first directory in GOPATH

When using GVM, my GOPATH had multiple directories in it and `cp`
in build.sh was failing as it was trying to copy to a non existent directory
due to the colons in the path
Note on binary copy

Update readme to note that `make` will copy the built binary into the first
part of the `$GOPATH`
Merge pull request #151 from extraordinaire/master

scripts: copy binary to first directory in GOPATH