Clarify BitPack is not for creating custom encodings

[DigitalBrains1]

It's easy to misconstrue the purpose of BitPack

Still TODO:

• Write a changelog entry (see changelog/README.md)
• Check copyright notices are up to date in edited files

[kleinreact]

Great to have it mentioned now. I only have some minor points:

• "not the way" is a little bit weak formulation, because it still suggests that it's fine to define custom instances overall. I would be more strict and use something link "You should never define a custom instance yourself, but instead use ... . The purpose of BitPack is to provide uniform conversion methods only.". I also liked your explanation that "It allows no creativity." of ILA ignores custom BitPack instances #2574.

• I also would mention that deriving (BitPack) is fine too. At the moment it may be missinterpreted that defining a custom representation is the only way.

• Rather than dictate what the bit representation in HDL is, a BitPack instance needs to exactly match that bit representation.

  I also got confused by that sentence, probably because its not immediately clear what "that bit representation" refers to.

[DigitalBrains1]

• Rather than dictate what the bit representation in HDL is, a BitPack instance needs to exactly match that bit representation.

I also got confused by that sentence, probably because its not immediately clear what "that bit representation" refers to.

I hoped it was clear that "that representation" in the second sentence fragment refers to "the representation" in the first sentence fragment, but would you rather see it repeated verbatim?

Rather than dictate what the bit representation in HDL is, a BitPack instance needs to exactly match the bit representation in HDL.

[kleinreact]

Rather than dictate what the bit representation in HDL is, a BitPack instance needs to exactly match the bit representation in HDL.

It still confuses me. Maybe, because "the bit representation" is just very generic: so maybe elaborating on what bit representation is meant? I mean: I get what you wanna say with the sentence, but I have to read it at least twice and need to parse it carfully to get the meaning.

[DigitalBrains1]

I'll rephrase entirely.

[kleinreact]

LGTM now.

[DigitalBrains1]

@mergify rebase