Specify algorithm for digit 11 and beyond

https://github.com/google/open-location-code/blob/main/docs/specification.md#code-precision mentions non-square areas starting at digit 11.

https://github.com/google/open-location-code/blob/main/docs/olc_definition.adoc also says
> From 11 digits on, a different algorithm is used. The areas are slightly larger but the advantage is that the codes are shorter.

Alas, neither documents give any algorithm. Even what digit goes into what box is never explained.