Added Altium Designer Libraries with SCH Symbol and Footprint

[aloysiousBenoy]

Updated README with instructions on usage

I intentionally left our 3D models for the sockets to avoid a potential license issue. Mentioned this in the README. I can add this back if you prefer it that way @daanpape

[aloysiousBenoy]

Should close #5

[stijn577]

Hey I talked to Daan and the sockets shouldn't be an issue, would be great if you could add them.

I also had some other remarks:

• Adding TX0 and RX0 to the pin names IO43 and IO44
• Adding pin electrical types in the schematic (Power ports are already correct, but RST can be Input, rest I/O) and make sure the RST pin shows up as active low.
• Change the filenames to something more concrete than LIB-..., I'd suggest a similar naming to the KiCAD files. Just "walter.SchLib" for the symbol and "walter-socket.PcbLib" for the footprint. If you could add a "walter-solder.PcbLib" file as well that would be greatly appreciated.
• Add the datasheet and ideally the Mouser part number to the symbol parameters.