Added README.md for FakeDS18B20 example

library/OneWireSlave/examples/FakeDS18B20/README.md

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+This is the **DS18B20** fake emulator provided with the original version of OneWireArduinoSlave.
+
+To make it working, connect :
+
+- a GND pin of your Uno to your 1-wire network ground.
+- the pin "2" of your Unto to the data line of your 1-wire network. You may use "3" as well but need to change the code.
+
+You will see 28.000000000002 probe that always return 42 as temperature :
+
+    $ cat 28.000000000002/temperature
+    42
+Notez-bien : conversion timing is emulated as well.