Fix a broken link.
The current layout does have a tab key.
One can get single keycaps from Signature Plastics.
Specify the kind of the mini USB cable needed.

Also: point out that thick USB cable connectors are trouble.
Add tables with row-to-pin and column-to-pin maps.
Check spelling; rephrase description of the wiring of thumb keys.
Merge pull request #3 from ckhroulev/tweaking-readme

Several minor improvements in README.org