Moved doc from UNB to RADIOHDL.

libraries/io/tr_xaui/doc/readme.txt

+How to compile the IP used by the tr_xaui module:
+=================================================
+1) Run the megawizard on the variation files, by:
+   . running 'unb_mgw tr_xaui' or
+   . running the MegaWizard GUI on /src/ip/megawizard/*vhd files
+2) In ModelSim, first compile the simulation libraries:
+   . lp tr_xaui
+   . In the project window, right-click the 'compile_ip' TCL scripts and
+     select 'execute'.
+3) Now the tr_xaui module itself can be compiled:
+   . mk compile