Update Readme

README.md

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 #Ethernet Library for Teensy#
 
+Wiznet chips W5100, W5200 and W5500 are automatically detected.  Efficient block transfer modes of W5200 and W5500 are utilized.
+
+Chip select must be connected to pin 10.  Reset for W5200 must be connected to pin 9.
+
+Wiznet socket status registers are cached, which greatly reduces SPI communication overhead, at the cost of a small increase in RAM usage.  TCP connections and UDP packets accessed in small chunks typically see a substantial performance boost.
+
 http://www.pjrc.com/teensy/td_libs_Ethernet.html
 
 ![](http://www.pjrc.com/store/wiz820_assem5.jpg)