Update README.rst
Update README.rst

Add gotcha: The content repository requires additional cygwin packages.
iot-factory/synapse,howethomas/synapse,rzr/synapse,howethomas/synapse,howethomas/synapse,matrix-org/synapse,matrix-org/synapse,illicitonion/synapse,iot-factory/synapse,matrix-org/synapse,iot-factory/synapse,howethomas/synapse,rzr/synapse,rzr/synapse,illicitonion/synapse,iot-factory/synapse,TribeMedia/synapse,matrix-org/synapse,matrix-org/synapse,rzr/synapse,illicitonion/synapse,TribeMedia/synapse,illicitonion/synapse,rzr/synapse,TribeMedia/synapse,TribeMedia/synapse,iot-factory/synapse,TribeMedia/synapse,illicitonion/synapse,matrix-org/synapse,howethomas/synapse