Need to update README.md with new Makefile

[johnnystarr]

On Master, your README.md states that to compile run make pdp7 however there is no target for this. This project is very exciting to me, however I cannot figure out how to follow the instructions. I can make all or make alt but can't really make heads or tails of how things work.

I have been able to load UNIX with SIMH 4.0 but I cannot follow the "hello world" instructions as the bc compiler is not present on the FS after booting. I can see that this might be part of the make alt subset targets, but running that does not compile bc for me.

I champion your efforts in this awesome project. But perhaps we can update the documents so the rest of us can enjoy this labor of love ;)

[johnnystarr]

I'd be happy to open a PR and update these changes if you can provide me a breakdown of what you're trying to accomplish with this Makefile. Thanks.

[johnnystarr]

I see a PR was opened to update the README but I’d really appreciate some feedback if possible. Thanks