[WIP] Update documentation to explain CANFD_BRS attribute

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

Original prompt

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This section details on the original issue you should resolve

<issue_title>dbc: Explain CANFD_BRS attribute</issue_title>
<issue_description>Is your feature request related to a problem? Please describe.
The message attribute VFrameFormat alone is under-specified, and always paired with the CANFD_BRS message attribute which is parsed additionally for messages of frame format StandardFD and ExtendedFD.

The difference between the StandardCAN and the StandardFD format is only whether the frame may make use of CAN FD extensions at all. Those extensions are:

• Extended data length codes
• The BRS bit in the CAN FD header is no longer "reserved" - this detail is quite important because setting this reserved bit in a frame of format StandardCAN will trigger an error frame in a compliant receiver.

In the opposite direction, StandardFD as frame format alone does not declare the value of the BRS bit.

Describe the solution you'd like
Correctly describe the CANFD_BRS message attribute in the list of "standard" message attributes, and its conditional relationship to the frame formats its applicable to.

It's typically defined as:

BA_DEF_ BO_  "CANFD_BRS" ENUM  "0","1";
BA_DEF_DEF "CANFD_BRS" "0";

The default varies between DBC that has been migrated from non-FD to FD ("0") and native FD networks ("1").

Describe alternatives you've considered
Well, you can't correctly communicate in an FD enabled networks if you don't understand the CANFD_BRS message attribute. Blindly enabling BRS just because a frame is using FD extensions just makes you a babbling idiot.

Additional context
Add any other context or screenshots about the feature request here.
</issue_description>

<agent_instructions>Improve the documentation in the nberlette/canbus repository to satisfy the user's grievances in issue #21. This includes updating the README, actual files in the repository (including .dbc files and docs files like markdown etc), and also the repository Wiki which includes documentation for a subset of the DBC format. While we're at it, please update the wiki with the areas of the DBC spec that are missing, and verify/update the existing pages, correcting any errors/typos/incorrect statements, and so on. Be sure to thoroughly explain each concept and include real-world examples of the related DBC syntax, where applicable. If you're using outside sources for your content, be sure to fully cite them (e.g., via markdown footnotes or a dedicated references/citations section at the bottom of each page), with the URL you sourced the content from. </agent_instructions>

Comments on the Issue (you are @copilot in this section)

@nberlette @Ext3h Thank you for catching that! The Wiki and reference are both very out of date, and you are correct in catching that erroneous piece of info in there.

I appreciate the detailed breakdown you gave, and I'm eager to update the repo with the latest, most accurate information available.

Unfortunately – like many of us – I just don't have enough hours in the day. If you'd be open to contributing this change in a PR that would be greatly appreciated! If not, that's totally understandable and I'll do my best to push a PR with the updates (and credit given to you) as soon as I can.

That being said, I'm definitely looking for additional collaborators who would be willing to help me move this project forward in the direction it needs to go.

If you'd be interested in helping with any of that, please shoot me an email and we'll discuss it further.

Thanks again!!
Nick </comment_new>

• Fixes dbc: Explain CANFD_BRS attribute #21

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