Fix installation diective

[wusatosi]

When running go get as suggested by readme, the go cmd returns:

go: go.mod file not found in current directory or any parent directory.
	'go get' is no longer supported outside a module.
	To build and install a command, use 'go install' with a version,
	like 'go install example.com/cmd@latest'
	For more information, see https://golang.org/doc/go-get-install-deprecatio

This pr updates the documentation to the go install interface as suggested by golang cmd