[1.6.x] Added link to localized formatting doc from main index.

abb04f1f3f from master.
[1.6.x] Fixed #21558 -- Support building CHM files.

Thanks Michał Pasternak.

Backport of cd9e85ec from master.
[1.6.x] Listed 1.6.x releases in descending order

Backport of 0daa2f1bf1 from master