added more interesting pdb entries

docs/interesting-pdb-entries.md

@@ -24,4 +24,5 @@
 * Close backbone atoms but not linked (e.g. 4HIV)
 * Non-standard residues
     * Protein (1BRR, 5Z6Y)
-    * DNA (5D3G)
+    * DNA (5D3G)
+* Multiple models with different sets of ligands or missing ligands (1J6T, 1VRC, 2ICY, 1O2F)