Documenting rule-of-thumb when optimizing DB usage with indexes...

[alextreme]

with a number of caveats to hopefully deter readers from using indexes everywhere. For ticket #21989

Based on #2252 from bbaja42

[colons]

Awesome.

[alextreme]

Thanks! Apologies for not conforming to the Django committing guidelines regarding my commit message, I will do so for future commits.

[charettes]

@alextreme it's not too late to change your commit message. You can simply use git commit --amend and force push your changes to your ticket-21986 branch.

[sergeykolosov]

Probably, it is also worth mentioning usages of Model.Meta.ordering, ModelAdmin.date_hierarchy, ModelAdmin.list_filter and ModelAdmin.ordering.

[timgraham]

merged in c8d61fa, thanks.