Added PrefGradeProfile to docs

docs/source/collective_decision_procedures.md

@@ -20,7 +20,7 @@ We further categorize collective decision procedures based on the input from the
       * [Probabilistic Methods](probabilistic_methods.md)
 
 
-  2. Cardinal procedures take as input a [UtilityProfile](utility_profiles.md) and/or a [GradeProfile](grade_profiles.md). These procedures are discussed in the following: 
+  2. Cardinal procedures take as input a [UtilityProfile](utility_profiles.md), a [GradeProfile](grade_profiles.md), and/or a [PrefGradeProfile](pref_grade_profiles.md). These procedures are discussed in the following:
 
       * [Utility Methods](utility_methods.md)
       * [Grade Methods](grade_methods.md)

docs/source/index.rst

@@ -111,6 +111,7 @@ Contents
    profiles_with_ties
    pairwise_profiles
    grade_profiles
+   pref_grade_profiles
    utility_profiles
    spatial_profiles
    weighted_majority_graphs

docs/source/pref_grade_profiles.md

@@ -0,0 +1,11 @@
+Pref Grade Profiles
+=======================================
+
+Profiles of voters that each submit both a (truncated) strict weak order and an assignment of grades from a fixed set to each candidate. The ballots for a PrefGradeProfile are [Rankings](ballots.md#ranking-class) and [Grades](ballots.md#grade-class).
+
+## PrefGradeProfile Class
+
+```{eval-rst}
+.. autoclass:: pref_voting.pref_grade_profile.PrefGradeProfile
+    :members:
+```