[DOC] Add a note in build instructions to be careful of Python packages in ~/.local/lib/pythonX.X/site-packages

[tmckayus]

Copies of cuopt Python dependencies (direct or indirect) in ~/.local/lib/pythonX.X/site-packages can cause build failures of the Python components for cuopt because Python will find these first before finding packages in the current conda environment.

The errors can be difficult to understand, for example an error in the ucxx package because it is referencing an attribute in the rmm package or subpackage which does not exist.

These errors persist even after creating a fresh conda environment and rebuilding. If this happens, then one likely cause is that there are conflicting packages under ~/.local/lib/pythonX.X/site-packages

How to repair:

1. review and remove unneeded packages under ~/.local/lib
2. create a new temporary user and try a build under that user or build on another system. If the problem persists, it is likely an upstream problem in the packages themselves. If the problem goes away, it is probably the ~/.local/lib.
3. backup and remove ~/.local/lib completely (it can be restored later, or selected libraries can be restored as needed)