settings: Document changing LOCAL_UPLOADS_DIR.
settings: Document changing LOCAL_UPLOADS_DIR.

The main point here is that you should use a symlink rather than
changing it, since it's more maintenance work to update our nginx
configuration to use an alternative path than to just create a
symbolic link.

Fixes #12157.

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