docs: Clarify push registration for running manage.py correctly.
docs: Clarify push registration for running manage.py correctly.

We've had several users get errors running this because they ran it as
a bash script; fix this my making the command super explicit.

dhcrzf/zulip,jackrzhang/zulip,hackerkid/zulip,shubhamdhama/zulip,jackrzhang/zulip,rht/zulip,zulip/zulip,shubhamdhama/zulip,showell/zulip,punchagan/zulip,showell/zulip,tommyip/zulip,timabbott/zulip,brainwane/zulip,synicalsyntax/zulip,punchagan/zulip,tommyip/zulip,kou/zulip,rishig/zulip,zulip/zulip,tommyip/zulip,rht/zulip,eeshangarg/zulip,rht/zulip,timabbott/zulip,rishig/zulip,rht/zulip,rishig/zulip,dhcrzf/zulip,andersk/zulip,punchagan/zulip,hackerkid/zulip,kou/zulip,timabbott/zulip,jackrzhang/zulip,eeshangarg/zulip,zulip/zulip,rishig/zulip,andersk/zulip,brainwane/zulip,synicalsyntax/zulip,tommyip/zulip,shubhamdhama/zulip,showell/zulip,synicalsyntax/zulip,shubhamdhama/zulip,brainwane/zulip,brainwane/zulip,jackrzhang/zulip,eeshangarg/zulip,andersk/zulip,hackerkid/zulip,shubhamdhama/zulip,timabbott/zulip,eeshangarg/zulip,andersk/zulip,zulip/zulip,andersk/zulip,eeshangarg/zulip,shubhamdhama/zulip,dhcrzf/zulip,timabbott/zulip,zulip/zulip,timabbott/zulip,andersk/zulip,kou/zulip,brainwane/zulip,tommyip/zulip,punchagan/zulip,hackerkid/zulip,hackerkid/zulip,andersk/zulip,rht/zulip,timabbott/zulip,zulip/zulip,jackrzhang/zulip,kou/zulip,punchagan/zulip,tommyip/zulip,hackerkid/zulip,dhcrzf/zulip,eeshangarg/zulip,hackerkid/zulip,rht/zulip,jackrzhang/zulip,zulip/zulip,kou/zulip,brainwane/zulip,showell/zulip,punchagan/zulip,dhcrzf/zulip,synicalsyntax/zulip,shubhamdhama/zulip,showell/zulip,jackrzhang/zulip,dhcrzf/zulip,brainwane/zulip,tommyip/zulip,showell/zulip,showell/zulip,eeshangarg/zulip,kou/zulip,rishig/zulip,rishig/zulip,punchagan/zulip,kou/zulip,synicalsyntax/zulip,synicalsyntax/zulip,synicalsyntax/zulip,rht/zulip,rishig/zulip,dhcrzf/zulip