index.md contained references to md files without file extensions, causing a 404 when clicked on github. Added file extensions.
index.md contained references to md files without file extensions, causing a 404 when clicked on github. Added file extensions.

Signed-off-by: Eric Lehmann <9390d8c1a94beed09d9d342d0ef76e29f3d67794@katyl.info>

Praqma/2git