graphgym: A correction in documentation and added information on how to install requirements

[rraadd88]

1. In the documentation of graphgym, configs/example_node.yaml should be configs/pyg/example_node.yaml, based on the current location of that file in the repository.
2. The documentation lacked information on how to install the requirements for graphgym. So I added a graphgym/configure.py file which extracts graphgym's requirements from the pyproject.toml. Accordingly, following line is added in the documentation:

python configure.py;pip install -r requirements.txt

I hope this helps.

[rraadd88]

example_node.yaml is located in pyg folder.

[rusty1s]

Thanks!

[rraadd88]

About pip install torch-geometric[graphgym], I wonder if running this command could replace the installed version of the package. I suppose one should have the same version of the package installed and the (git-)cloned to use graphgym. But if this is not the case, users could lose their installed version of pyg.

I had suggested separating the requirements from toml and installing them, for this reason. By installing only the requirements, users would not lose their installed version of pyg.

[rusty1s]

IMO, it will not override the existing version of the package. This is definitely the recommended way to install the missing dependencies. I personally would like to avoid adding a script that parses the toml and creates a requirement file from it.