docs: Suggest updating settings.py in OIDC instructions.
docs: Suggest updating settings.py in OIDC instructions.

OIDC config features a get_secret call (so it requires adding an import)
as well as having a bunch of its instructions in the form of comments on
the various keys of the config dict - thus users should really update
settings.py to fetch all of that.

eeshangarg/zulip,rht/zulip,andersk/zulip,andersk/zulip,kou/zulip,andersk/zulip,rht/zulip,rht/zulip,kou/zulip,zulip/zulip,rht/zulip,zulip/zulip,eeshangarg/zulip,kou/zulip,rht/zulip,rht/zulip,andersk/zulip,andersk/zulip,eeshangarg/zulip,kou/zulip,eeshangarg/zulip,zulip/zulip,zulip/zulip,andersk/zulip,rht/zulip,andersk/zulip,zulip/zulip,kou/zulip,eeshangarg/zulip,kou/zulip,zulip/zulip,kou/zulip,eeshangarg/zulip,eeshangarg/zulip,zulip/zulip