[spinel] add spinel definition guideline (#3663)
[spinel] add spinel definition guideline (#3663)


lanyuwen/openthread,turon/openthread,bukepo/openthread,chshu/openthread,lanyuwen/openthread,srickardti/openthread,abtink/openthread,librasungirl/openthread,bukepo/openthread,abtink/openthread,librasungirl/openthread,jwhui/openthread,bukepo/openthread,chshu/openthread,turon/openthread,lanyuwen/openthread,openthread/openthread,openthread/openthread,chshu/openthread,openthread/openthread,openthread/openthread,lanyuwen/openthread,chshu/openthread,srickardti/openthread,librasungirl/openthread,jwhui/openthread,jwhui/openthread,librasungirl/openthread,jwhui/openthread,turon/openthread,srickardti/openthread,abtink/openthread,chshu/openthread,lanyuwen/openthread,lanyuwen/openthread,srickardti/openthread,chshu/openthread,turon/openthread,abtink/openthread,bukepo/openthread