Propose tracking of sources

[RobertBaruch]

To @DIYsciBorg's comment on tracking from Issue 5, I can see some possibilities:

• For schematics, require a readme.md that includes the source(s) of schematics (even if "reverse engineered by me"). Sources which are online must either already be on the Internet Archive, or uploaded to the Internet Archive, and must include at least one URL pointing to the Internet Archive.

• Symbols not present in the current KiCAD release must be created and placed in a new library added to bit-preserve, or an existing library on bit-preserve.

• New symbols must conform to the KiCAD library standard. That also means including URLs for datasheets, preferably pointing to the Internet Archive. You can instead try to add the symbol to the KiCAD libraries, but it can take a while to get a component through the KiCAD pull request process. Schematics use the -cache.lib file for symbols anyway, so it's ok to use a library on bit-preserve.