make build: added simple target "help"
make build: added simple target "help"

'make help' prints now some important commands (make targets).

Signed-off-by: Jasmin Jessich <839fc0942a91298ad0e933ade35eca7597b1eb88@anw.at>
[877e75d40d628e7703cdd959d7738e63d8f6e612@distortec.com: minor formating/editorial changes]
Signed-off-by: Kamil Szczygiel <877e75d40d628e7703cdd959d7738e63d8f6e612@distortec.com>
CezaryGapinski/distortos,jasmin-j/distortos,jasmin-j/distortos,DISTORTEC/distortos,jasmin-j/distortos,CezaryGapinski/distortos,DISTORTEC/distortos,DISTORTEC/distortos,CezaryGapinski/distortos,jasmin-j/distortos,DISTORTEC/distortos,CezaryGapinski/distortos,jasmin-j/distortos,CezaryGapinski/distortos