Add CHANGELOG for alpha20
Add CHANGELOG for alpha20

Khaledgarbaya/gatsby,fk/gatsby,chiedo/gatsby,mingaldrichgan/gatsby,fabrictech/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,mingaldrichgan/gatsby,chiedo/gatsby,ChristopherBiscardi/gatsby,mickeyreiss/gatsby,fk/gatsby,danielfarrell/gatsby,chiedo/gatsby,danielfarrell/gatsby,mingaldrichgan/gatsby,mickeyreiss/gatsby,gatsbyjs/gatsby,fabrictech/gatsby,fk/gatsby,okcoker/gatsby,0x80/gatsby,ChristopherBiscardi/gatsby,okcoker/gatsby,ChristopherBiscardi/gatsby,okcoker/gatsby,gatsbyjs/gatsby,mickeyreiss/gatsby,Khaledgarbaya/gatsby,fabrictech/gatsby,0x80/gatsby,Khaledgarbaya/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,0x80/gatsby,danielfarrell/gatsby