Undocumented dependencies: gcc-c++ and python3-devel (on Linux)

[aseyffert]

(I'm running Fedora Linux 37, and installing into a virtual environment provided by python's venv module. My python version is 3.11.6.)

I followed the installation instructions in README.md, but the build failed for celerite2, mphs, and P4J. These seem to be the only components that are compiled from source.

I worked through the tracebacks, did some digging, and resolved the issue by installing (via Fedora's repos):

• gcc-c++, which provides a C++ compiler, and
• python3-devel, which provides the necessary C++ header file(s); specifically: Python.h, but there might be others. (This must be installed prior to the creation of the venv virtual environment, since the header files are copied into the environment when it is created.)

Perhaps these dependencies can be documented in README.md?

(NOTE: I've yet to confirm that lc_classifier works as expected after this installation.)