Update install instructions and recommendations

This PR contains no actual changes to the PyMAD code, rather:

- fix minor syntax errors in the installation/index.rst file (some content
  was not showing in output)
- recommend to use static MAD-X build on windows. This is most convenient
  way to link on windows. It is made possible by the restriction to a
  single Python file that links to MAD-X.
- make missing .c file error more explicit