WIP: Add initial elements documentation

Attempt to capture what elements are acquired and derived, and information about how channels are derived.

@pcain, @erigler : let me know your thoughts on this, it's definitely incomplete. I'd like to finish some form of this documentation before reviewing the processing updates.

I'm not sure why GitLab provides so much context for each of my comments. It seemed to me that it was only associating my comments with a single line of code. Let me know if you aren't certain which line of the MD file I was referring to with each comment.

@pcain , @erigler : note that when adding comments to issues you can select the drop down on the "Comment" button and change it to "Start thread" so we can have a threaded discussion that needs to be resolved. This is the default when commenting on code, but also useful for non-code discussions

Something that arose when writing pipeline updates, which I am also seeing here, is the difference between base miniseed/edge channels as they are used to calculate derived channels. For instance:

---

Adjusted Algorithm:

Legacy: HEZF -> XYZF

Miniseed: UVWF -> XYWF

---

XYZAlgorithm:

Legacy: XYZF -> D

Miniseed: XYWF -> D

---

XYZAlgorithm(adjusted data type):

Legacy: XYZF -> H D

Miniseed: XYWF -> U D

---

If we want to process pure miniseed, then it would be a good idea to no longer describe outputs as the old SNCL channels. However, there's an opportunity to keep a channel like Z as it may be more descriptive than the raw variation channel. If we don't want to make this step right now, I can revert the changes to process using the edge factory/legacy sncls instead

mentioned in merge request !100 (closed)

mentioned in issue #35 (closed)

mentioned in merge request !101 (merged)

resolved all threads

Moved to !101 (merged)

closed