Readme.JTAG_Timing

For JTAG Timing example, look e.g. at

http://pdfserv.maxim-ic.com/en/ds/DS4550.pdf
or
http://www.xilinx.com/support/documentation/application_notes/xapp070.pdf

This concludes to:
- Change TDI with the negative edge
- Sample TDO at the negative edge