Mention SyTest in the README, after Development
Mention SyTest in the README, after Development

Signed-off-by: Andrew Conrad <d1fa4d07ec1ca9e0c0754e6fade32c51e2055067@gmail.com>

matrix-org/synapse,matrix-org/synapse,matrix-org/synapse,matrix-org/synapse,matrix-org/synapse,matrix-org/synapse