Update RELEASENOTES-DEVELOPMENT.md

RELEASENOTES-DEVELOPMENT.md

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 Version 3.3.7d9
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 **Enhancements**
-* Improved timing estimation. Shairport Sync has been using linear least-squares regression to estimate timing drift between the (remote) source clock and the local clock. This technique is now extended to provide an estimate of the remote-to-local clock difference, used to remap the timing of audio frames from the remote device's clock to the local clock.
+* Improved timing estimation. Shairport Sync has been using linear least-squares regression to estimate timing drift between the (remote) source clock and the local clock. This technique is now extended to provide an estimate of the remote-to-local clock difference itself. The remote-to-local clock difference is used to remap the timing of audio frames from the remote device's clock to the local clock.
 
-  In practice, the timing technique in use up to now has been very accurate, but this should result in slightly smoother rates of correction. 
+  Timing drift estimates are now saved when a sessions ends, keyed to the client IP number. When a new session starts from that IP number, the stored estimate is used until a new estimate can be generated from the new session.
+
+  In practice, the timing techniques in use up to now have been very accurate, but this should result in slightly smoother rates of correction. 
 
 Version 3.3.7d8
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