The meaning of hint files is explained in

https://sympa.inria.fr/sympa/arc/cado-nfs/2020-04/msg00019.html

Here is the meaning of a hint file line :
21@1 1 1 I=11 20000,18,36 20000,18,36

To descend a special-q of 21 bits on side 1, use a sieve with
I=11
lim0=lim1=20000
lpb0=lpb1=18
mfb0=mfb1=36
the first block 20000,18,36 corresponding to side0 and the second to
side1.

The "1 1" in second and third positions can be safely ignored.

Each line gives therefore a rule about how to handle a node in the
descent tree.
