Update README.md

Corrects the README for fpm install via homebrew

Author: pgierz

README.md

@@ -5,7 +5,7 @@ This repository provides package build instructions for tools and libraries arou
 For example you can install *fpm* by tapping this repository
 
 ```
-brew tap fortran-lang/fortran
+brew tap fortran-lang/homebrew-fortran
 brew install fpm
 ```