Prepare release notes for 0.4.20 (hyperledger-labs#2615)

[static]

Signed-off-by: Moritz Kiefer <moritz.kiefer@purelyfunctional.org>
Co-authored-by: Moritz Kiefer <moritz.kiefer@purelyfunctional.org>

Author: moritzkiefer-da

docs/src/release_notes.rst

@@ -8,8 +8,8 @@
 Release Notes
 =============
 
-Upcoming
---------
+0.4.20
+------
 
   - Deployment