Update release notes

Author: xispa

RELEASE_NOTES.rst

@@ -1,6 +1,21 @@
 Release notes
 =============
 
+Update from 2.0.0 to 2.1.0
+--------------------------
+
+!!! This update requires at least Plone 5.2.5 and Python 2.x. !!!
+
+Please update your `buildout.cfg` configuration file to this version and re-run
+the `buildout` script.
+
+You can use the Plone unified installer to install Plone 5.x first:
+https://github.com/plone/Installers-UnifiedInstaller
+
+Please make sure to pin `senaite.lims` to version `2.1.0` to get the correct
+versions of all dependent SENAITE packages.
+
+
 Update from 1.3.x to 2.0.0
 --------------------------
 
@@ -18,7 +33,6 @@ versions of all dependent SENAITE packages.
 Run first the Plone upgrade before you continue to update SENAITE to version 2.x.
 
 
-
 Update from 1.3.0 to 1.3.1
 --------------------------