Hi everyone!

As a follow up to https://review.coreboot.org/c/flashrom/+/58477 and https://review.coreboot.org/c/flashrom/+/58480, I want to update the section "Adding/reviewing a new flash chip" of the dev guidelines with documentation for two new chip data fields that were added:

`.reg_bits` stores information about what configuration bits the chip has and where they are found. For example,`.cmp = {STATUS2, 6, RW}` indicates that the chip has a complement bit (CMP) and it is the 6th bit of the 2nd status register. See `struct reg_bit_info` in flash.h for details on each of the structure's fields.

Note that some chips have configuration bits that function like TB/SEC/CMP but are called something else in the datasheet (e.g. BP3/BP4/...). These bits should be assigned to a field according their function and the datasheet name should be noted in a comment, for example:
```
.sec = {STATUS1, 6, RW}, /* Called BP4 in datasheet, acts like SEC */
```

`.decode_range` points to a function that determines what protection range will be selected by particular configuration bit values. It is required for writeprotect operations on the chip.

Let me know if the text is alright, thanks!

Cheers,

Nik