It contained outdated information about attaching patches to bug
reports. Shorten it to the essentials.
Also format it using markdown and rename it to CONTRIBUTING.md, which is
a convention and doesn't include "patches" in the name.
Change-Id: I9ee73f16e6fa8fbf529ac0ca791e2375d4d56d68
Signed-off-by: Robin Stocker <robin@nibor.org>