Document how the tables are constructed

[Sjlver]

Something like this (from https://news.ycombinator.com/item?id=38963197)

The 25 rows of the table correspond to the 25 linear polynomials in GF(5), evaluated at x=0, 1, 2, 3, and 4.
GF(5) is the "field" that psst uses. It just means that all math is performed using only digits 0 to 4, and we take the remainder modulo 5 after each operation. A linear polynomial has the form ax + b. There are 25 of them because a and b can each take one of the five values.

For example, consider the polynomial 3x + 0. If you evaluate it at x=0, the result is 0. At x=1, it's 3. At x=2, it's 6, which corresponds to 1 in GF(5). At x=3, the result is 4, and at x=4, the result is 2. These values (0 3 1 4 2) form the fourth line in the table above.

The table on the first page of the worksheet and the table on each share all have the same rows. They are just sorted differently, to make it easier to lookup a given row.