README.md suggests building with make rather than Hadrian

Summary

Location of documentation issue: (e.g. the Haddocks of base, the GHC user's guide)

In README.md, the "quickstart" section

Write a brief description of the issue.

The list of quick start commands is ./boot, ./configure, and then make and make install.

Proposed improvements or changes

I propose that it should be updated to suggest Hadrian instead.

Environment

• GHC version used (if appropriate): The latest development version