interfaces: update README.md (#36)

use go install instead of go get due to https://go.dev/doc/go-get-install-deprecation

Author: wirekang

README.md

@@ -12,7 +12,7 @@ Generates an interface for a named type.
 
 *Installation*
 ```bash
-~ $ go get github.com/rjeczalik/interfaces/cmd/interfacer
+~ $ go install github.com/rjeczalik/interfaces/cmd/interfacer@latest
 ```
 
 *Usage*