Improve the developer quickstart documentation

[JeanChristopheMorinPerso]

As note in https://academysoftwarefdn.slack.com/archives/CMQ9J4BQC/p1636760978147000, the developer quickstart documentation is out of date right now.

This PR removes obsolete instructions, adds some more instructions and also use modern methodologies (e.g. call python -m pip install of pip, don't call python setup.py, etc).

Hopefully it should be clear enough and the additions I made will help future contributors.

[JeanChristopheMorinPerso]

@ThomasWilshaw Do you think the proposed changed would have made your experience better?

[meshula]

Thanks for the update! I've noted a couple of issues.

[ThomasWilshaw]

@ThomasWilshaw Do you think the proposed changed would have made your experience better?

Yes that's definitely clearer but there's still a few things I don't follow.

1. In the section "To build OTIO for Python development", where is the given command meant to be run from? The source directory or somewhere else? Also is a note of what the --user option does necessary or will most people know what it's for already?

2. In the section: "To build OTIO for both C++ and Python development" it implies that you should run setup.py to create all the build files and compile OTIO, is that what we have just done in the previous step when we ran python -m pip install . --user? It also says using setup.py is highly discouraged, despite just saying to run it.

Am I right in thinking that if I were to edit the code base in a way that affected both the Python and C++ sections, the best way for me to compile everything and run the tests would be to run python -m pip install. --user whereas if I were just modifying the C++ code I should use the standard cmake --build... command?

I should just clarify I'm not a very experienced dev (and I particularly don't like actually compiling software ;)) so I could just be misunderstanding things or generally no know what I'm doing :)

[JeanChristopheMorinPerso]

@ThomasWilshaw I just pushed an update which hopefully should answer your questions. Let me know if it's still unclear.

[meshula]

One thing we haven't gotten to is a comprehensive test suite at the C++ level. We are relying on the python bindings to expose problems. If you are developing in the C++ code, you should do a pip install and run the python tests before submitting a PR. It's up to you whether you also do a pip install while you are iterating the C++ code.

New C++ PRs are expected to have a C++ based test to go along with them. We will need to add a comprehensive test suite at the C++ level.

[ThomasWilshaw]

@ThomasWilshaw I just pushed an update which hopefully should answer your questions. Let me know if it's still unclear.

That's defintely a lot clearer thanks.