README: improve formatting of important files

Previously, this entire block was in a script block.  This looked shitty.

Now it's an unordered list (since it's an unordered list), and only the filenames are monospaced.  This sets them apart from the text describing them, making everything easier to read.
Merge pull request #5 from xiongchiamiov/patch-1

README: improve formatting of important files