add git step to heroku guide
add git step to heroku guide

gavinwye/govuk_prototype_kit,tsmorgan/marx,joelanman/govuk_prototype_kit,davedark/proto-timeline,benjeffreys/hmcts-idam-proto,paulpod/invgov,joelanman/govuk_prototype_kit,chrishanes/pvb_prisoner_proto,davedark/proto-timeline,tsmorgan/marx,DilwoarH/GDS-Prototype-DM-SavedSearch,benjeffreys/hmcts-idam-proto,hannalaakso/accessible-timeout-warning,hannalaakso/accessible-timeout-warning,samwake/hoddat-cofc-caseworking,dwpdigitaltech/hrt-prototype,abbott567/govuk_prototype_kit,paulpod/invgov,abbott567/govuk_prototype_kit,dwpdigitaltech/hrt-prototype,arminio/govuk_prototype_kit,DilwoarH/GDS-Prototype-DM-SavedSearch,alphagov/govuk_prototype_kit,DilwoarH/GDS-Prototype-DM-SavedSearch,samwake/hoddat-cofc-caseworking,nhsbsa/ppc-prototype,nhsbsa/ppc-prototype,nhsbsa/ppc-prototype,chrishanes/pvb_prisoner_proto,samwake/hoddat-cofc-caseworking,Demwunz/esif-prototype,chrishanes/pvb_prisoner_proto,dwpdigitaltech/hrt-prototype,benjeffreys/hmcts-idam-proto,hannalaakso/accessible-timeout-warning,arminio/govuk_prototype_kit,alphagov/govuk_prototype_kit,alphagov/govuk_prototype_kit,gavinwye/govuk_prototype_kit,arminio/govuk_prototype_kit,joelanman/govuk_prototype_kit,davedark/proto-timeline,Demwunz/esif-prototype,Demwunz/esif-prototype,paulpod/invgov,tsmorgan/marx,abbott567/govuk_prototype_kit