Update README.rst

Author: jmmshn

README.rst

@@ -53,6 +53,12 @@ identify the defect position in a simulation cell.
 Note, this method only requires the reference pristine supercell and does not need prior knowledge
 of how the defect was created.
 
+Defect Complexes
++++++++++++++++
+
+Multiple defects can be composed into defect complexes.
+The complex is can be treateded as a normal defect object for subsequent analysis.
+
 Capture coefficients
 ++++++++++++++++++++