Outdated installation instructions

[shining-fnml]

The "Installing" section in the README.md suggests to run "go get -u github.com/erincandescent/nuvoprog".
In go 1.18 this raises the following error:

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-deprecation
or run 'go help get' or 'go help install'.