README.md: minor fixes
README.md: minor fixes

Previously header level h3 was not used - change h4 and h5 to h3 and h4
respectively.

Don't indent multiline list items - this sometimes causes strange
display in Eclipse.
CezaryGapinski/distortos,jasmin-j/distortos,jasmin-j/distortos,jasmin-j/distortos,DISTORTEC/distortos,jasmin-j/distortos,DISTORTEC/distortos,DISTORTEC/distortos,CezaryGapinski/distortos,jasmin-j/distortos,CezaryGapinski/distortos,CezaryGapinski/distortos,CezaryGapinski/distortos,DISTORTEC/distortos