Use go get in README

Closes #29

README.md

@@ -40,8 +40,8 @@ brew install nss # if you use Firefox
 On Linux (`-install` support coming soon!), use [the pre-built binaries (again, coming soon)](https://github.com/FiloSottile/mkcert/releases), or build from source (requires Go 1.10+).
 
 ```
-$ git clone https://github.com/FiloSottile/mkcert
-$ cd mkcert && make
+go get -u github.com/FiloSottile/mkcert
+$(go env GOPATH)/bin/mkcert
 ```
 
 Windows will be supported next.