Docs - relax strict requirement for SC synthdefs

Previously we said that only new synthdefs designed in SuperCollider were
considered for distribution in Sonic Pi. We now tone that down to state that it
is 'strongly recommended' to use SuperCollider instead.

SYNTH_DESIGN.md

@@ -21,11 +21,11 @@ etc/synthdefs/designs/
 
 Most of these were originally designed in Overtone. **_Please note however_**,
 that for _new_ synth designs _that are intended to be distributed with Sonic
-Pi_, source code written with Overtone is now considered deprecated and only
-designs written in SuperCollider language will be accepted. As such, the
-instructions for using Overtone still work, but if you are considering
-submitting a new synth design for distribution with Sonic Pi, please create your
-synth with SuperCollider directly.
+Pi_,the preference is that they are created with SuperCollider, as it is much
+easier to set up, create and maintain synths this way. As such, the instructions
+for using Overtone still work, but if you are considering submitting a new synth
+design for distribution with Sonic Pi, we strongly recommend that you create
+your synth with SuperCollider directly.
 
 (Note also that detailed information on Overtone and SuperCollider syntax is
 beyond the scope of this document. However, the information contained below