cosmetics

[gkasprow]

@tprzywoz

• do not place fabrication files in the repo. Use releases, as we do in other SInara projects. All pdf, gerbers etc go there. The release is bonded to the commit number.
• missing description of critical components: trimpots (add short info like "5V current"), some test points, programmer connectors. Describe their function, not only designator
• avoid placing solid copper below pins like here
  
  This will confuse the AOI test. Don't have to fix them right now.
  -In next release place thermal conducting copper strip not only on top and bottom, but also on 2 inner layers to lower the thermal resistance.
  After fixing silkscreen info, send link to the production files directly to the manufacturer.

[tprzywoz]

Added description: 4x trimpots, MMC and FPGA JTAG connectors, 2x test points.
Fabrication files go to release assets (no update in commit).