Adds README.chromium for third-party integration.
Adds README.chromium for third-party integration.

ppy/angle,vvuk/angle,domokit/waterfall,MIPS/external-chromium_org-third_party-angle,mikolalysenko/angle,crezefire/angle,mrobinson/rust-angle,mrobinson/rust-angle,nandhanurrevanth/angle,bsergean/angle,jgcaaprom/android_external_chromium_org_third_party_angle,mikolalysenko/angle,jgcaaprom/android_external_chromium_org_third_party_angle,csa7mdm/angle,mikolalysenko/angle,jgcaaprom/android_external_chromium_org_third_party_angle,ppy/angle,csa7mdm/angle,mybios/angle,ecoal95/angle,vvuk/angle,mlfarrell/angle,bsergean/angle,ppy/angle,ghostoy/angle,larsbergstrom/angle,crezefire/angle,nandhanurrevanth/angle,csa7mdm/angle,MSOpenTech/angle,geekboxzone/lollipop_external_chromium_org_third_party_angle,android-ia/platform_external_chromium_org_third_party_angle,MIPS/external-chromium_org-third_party-angle,ghostoy/angle,mlfarrell/angle,nandhanurrevanth/angle,mybios/angle,larsbergstrom/angle,larsbergstrom/angle,android-ia/platform_external_chromium_org_third_party_angle,mlfarrell/angle,bsergean/angle,ppy/angle,MIPS/external-chromium_org-third_party-angle,mybios/angle,MSOpenTech/angle,geekboxzone/lollipop_external_chromium_org_third_party_angle,nandhanurrevanth/angle,ghostoy/angle,xin3liang/platform_external_chromium_org_third_party_angle,geekboxzone/lollipop_external_chromium_org_third_party_angle,xin3liang/platform_external_chromium_org_third_party_angle,csa7mdm/angle,MSOpenTech/angle,mybios/angle,ghostoy/angle,mrobinson/rust-angle,domokit/waterfall,mrobinson/rust-angle,crezefire/angle,bsergean/angle,crezefire/angle,vvuk/angle,android-ia/platform_external_chromium_org_third_party_angle,ecoal95/angle,mrobinson/rust-angle,larsbergstrom/angle,MIPS/external-chromium_org-third_party-angle,android-ia/platform_external_chromium_org_third_party_angle,ecoal95/angle,MSOpenTech/angle,vvuk/angle,geekboxzone/lollipop_external_chromium_org_third_party_angle,xin3liang/platform_external_chromium_org_third_party_angle,ecoal95/angle,jgcaaprom/android_external_chromium_org_third_party_angle,xin3liang/platform_external_chromium_org_third_party_angle,mlfarrell/angle,mikolalysenko/angle,ecoal95/angle