Expand installation instructions

[CEA-jiangming]

Install codex-africanus via pip install codex-africanus[complete] failed as dependencies wcslib and cfitsio could not be installed automatically.

[sjperkins]

Please post a stack trace

[CEA-jiangming]

Sorry, I didn't save the stack trace. It was a problem that it couldn't find wcslib.h and fitsio.h. I fixed this problem manually. Today I tried to install africanus on another machine but I didn't find this problem. Maybe it was related to python-casacore and the python version I used on my machine.

[sjperkins]

Ah yes, python-casacore builds from source and for that it needs casacore. Visit the casacore and python-casacore githubs for the required libraries and further installation instructions. Or just install kernsuite.

[sjperkins]

Reopening this as a documentation install issue.