Installing CadQuery with Pip3 on arm64 Apple M1

Just posting this here for future reference, as I couldn't find this solution anywhere in the README or in past issues on this topic.

I was able to install cadquery on my M1 Mac using the following steps:

1. Make sure Xcode command line tools and Python3 are installed (assuming you are not using *conda)
2. Upgrade pip like `python3 -m pip install --upgrade pip`
3. Add the following `requirements.txt` to your project:
```
cadquery
cadquery-ocp == 7.7.1
pyparsing >= 2.1.9
sphinx == 5.0.1
sphinx_rtd_theme
black == 19.10b0
click == 8.0.4
mypy
codecov
pytest
pytest-cov
ezdxf
typing_extensions
nptyping == 2.0.1
nlopt
path
casadi
multimethod >= 1.7,<2.0
typish
```
4. Install the intel versions of these packages: `arch -arch x86_64 pip3 install -r requirements.txt`
5. Run the intel version of cadquery and check that it's working:
```
arch -arch x86_64 python3
>>> import cadquery
>>> cadquery.Workplane('XY').box(1,2,3).toSvg()
```

Review the README, which currently does not describe the arm64 Apple M1 installation path. Use the listed Python, pip3, and arch commands as the source for a concise installation note, and verify that the documented commands install CadQuery and allow the shown Workplane box and toSvg check to run.

Written by the indexing model from the issue text.