Update mixins.json
Update mixins.json

Updating to add comments and clarity on what cannot be submitted
ENCODE-DCC/encoded,ENCODE-DCC/encoded,T2DREAM/t2dream-portal,T2DREAM/t2dream-portal,ENCODE-DCC/encoded,T2DREAM/t2dream-portal,ENCODE-DCC/encoded,T2DREAM/t2dream-portal