Update RELEASE_NOTES.md

Author: sergey-tihon

RELEASE_NOTES.md

@@ -1,9 +1,10 @@
-#### 3.0.0 - 2021-09-xx (unreleased)
+#### 3.0.0 - 2021-10-22
 * Deque.Tail performance tweaks
 * Fast path for single back element. Avoid traversing list for length multiple times. Use Unchecked.defaultOf<_> rather than an actual element. Thanks @simendsjo
 * Expose PersistentVector.rangedIterator. Thanks @simendsjo
 * Seq extensions: add tryHeadTail #176. Thanks @knocte
 * some helper functions #92. Thanks @sideeffffect
+* Enable PersistentVector in Fable #182. Thanks @njlr
 * Dependencies update
 * Build and test with .NET 5 & Node 14