code: def describe_features(self, traj):
          
          all_res = []
          for feat in self.which_feat:
              all_res.extend(self.features[feat].describe_features(traj))
          return all_res
docs: Return a list of dictionaries describing the features. Follows
          the ordering of featurizers in self.which_feat.
  
          Parameters
          ----------
          traj : mdtraj.Trajectory
              The trajectory to describe
  
          Returns
          -------
          feature_descs : list of dict
              Dictionary describing each feature with the following information
              about the atoms participating in each feature
                  - resnames: unique names of residues
                  - atominds: atom indicies involved in the feature
                  - resseqs: unique residue sequence ids (not necessarily
                    0-indexed)
                  - resids: unique residue ids (0-indexed)
                  - featurizer: featurizer dependent
                  - featuregroup: other info for the featurizer