Update CONTRIBUTING.md
Update CONTRIBUTING.md

Fixed the headers. They were rendering incorrectly on GitHub for some weird reason; I copied the strings and rewrote the ## characters at the beginning and now they render as they should.

Signed-off-by: Per Lundberg <7ca15d0b8f346535728b77efc7f6a5a27b3be4c4@ecraft.com>

dmcgowan/distribution,sadlil/distribution,jwhonce/distribution,manoj535/distribution,jwhonce/distribution,sergeyfd/distribution,docker/distribution,miminar/distribution,konstruktoid/distribution,yuwaMSFT2/distribution,mikebrow/distribution,docker/distribution,thaJeztah/distribution,vdemeester/distribution,estesp/distribution,konstruktoid/distribution,estesp/distribution,thaJeztah/distribution,sergeyfd/distribution,vdemeester/distribution,mikebrow/distribution,manoj535/distribution,dmcgowan/distribution,yuwaMSFT2/distribution,duglin/distribution,miminar/distribution,duglin/distribution,sadlil/distribution