Add separate install instructions for macOS Arm64 users in readme

[bobleesj]

Closes #86
Closes #24

Here is the rendered version of the REAMDE:

https://github.com/bobleesj/diffpy.pdffit2/tree/readme-install?tab=readme-ov-file#installation

[bobleesj]

@sbillinge ready for review - Codecov error is occuring for some reason. I will address it in the next PR.

[bobleesj]

I will try to re-run the CI with an empty commit.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.96%. Comparing base (cf12149) to head (207fb45).
Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #105   +/-   ##
=======================================
  Coverage   98.96%   98.96%           
=======================================
  Files           6        6           
  Lines        1261     1261           
=======================================
  Hits         1248     1248           
  Misses         13       13           

[bobleesj]

@sbillinge okay.. it was a glitch. Codecov works now.

[sbillinge]

let's remove this from the installation in the readme (and the docs if it is there), it is just confusing:

diffpy.pdffit2 supports Python 3.11 and 3.12 the following external software:

setuptools - software distribution tools for Python
python-dev - header files for interfacing Python with C
GSL - GNU Scientific Library for C
g++ - GNU C++ compiler
diffpy.structure - simple storage and manipulation of atomic structures, https://github.com/diffpy/diffpy.structure

Also, something happened to the rendering of the "conda config --add channels conda-forge".

Other than that it looks great!

[bobleesj]

@sbillinge Got it. the conda config --add channels conda-forge" is fixed and also removed dependencies for building.

[sbillinge]

Nicely done. Let me know when we are ready for PDFgui/PDF fit 2 release.