BigInt: Add technical description
The current draft chip is somewhat generic and considers the basics of going to any 64bit or higher setup, but does not have an actual clear proposal. It is my understanding that tobias rust and mark lunderberg have spent significant effort into this matter and that the current viewpoint can be seen in this code: https://github.com/cashweb/cashd/pull/71
In order to get something concrete into the chip, it would be good if we could at least get a bullet-point list or similar of the actual changes that 63bit+sign bit change results in. Additional information, such as a rational or laymans explanation of the change would also be welcome, but is not a requirement to get the chip published.
If it turns out that there is a better choice for the number of bits or the implementation, then we can still update the chip if sentiment changes, we just need something out now that interested people can provide feedback on.