Added a note wrt exFAT vs FAT32 since it causes the installer to fail.

Funny thing is that this only seems to happen on ppl using windows.
Added a note about the warning messages during installation.
Changed the formatting of the previous notes from italic to bold.
Improved the documentation for specifying the bootsize and rootsize parameters.

This fixes issue #144
Created the CONTRIBUTING document.

This should close #84.