update release notes

ReleaseNotes.md

@@ -7,8 +7,9 @@
   5), I (now 1, 3, 5), At (now 1, 3, 5), Xe (now 0, 2, 4, 6), and Po (now 2, 4,
   6). Molecules with atoms in the new valence states will no longer generate
   sanitization errors. Note that this has an impact on the chemistry of
-  molecules containing 3-valent I (present 21 times in ChEMBL 26): previously
-  this was incorrectly assigned two implicit Hs, now it has no implicit Hs. 
+  molecules containing 3-valent I and at least one implict H (present 24 times
+  in ChEMBL 27): previously this was incorrectly assigned two implicit Hs, now
+  it has no implicit Hs. 
 - Aromaticity perception of molecules like `Cc1nnc2n1c1ccccc1n1c(C)nnc12` now
   correctly recognizes the full outer envelope, i.e. the bonds joining the rings
   are now also aromatic.
@@ -54,6 +55,8 @@
   on atoms and bonds.
 - There's a new rdDeprotect module to allow automatically deprotecting molecules
   before putting them into reactions
+- Molecule and reaction metadata can now be added to PNG files generated by
+  MolDraw2DCairo
 
 ## Acknowledgements
 Shrey Aryan, Jinserk Baik, Francois Berenger, Cédric Bouysset, David Cosgrove,