Adds Docs to Const Type

docs/source/usage.const.rst

@@ -0,0 +1,40 @@
+Const Type
+=================
+
+The const type is a special data type that allows a variable to be a single, fixed value.
+It does not have the same properties as the other generic types, but it has the following specific properties:
+
+- const: The fixed value that the variable must always hold.
+- description: Description of the const field.
+
+
+Examples
+-----------------
+
+
+.. code-block:: python
+    
+    from jambo import SchemaConverter
+
+
+    schema = {
+        "title": "Country",
+        "type": "object",
+        "properties": {
+            "name": {
+                "const": "United States of America",
+            }
+        },
+        "required": ["name"],
+    }
+
+    Model = SchemaConverter.build(schema)
+
+    obj = Model()
+    self.assertEqual(obj.name, "United States of America")
+
+    with self.assertRaises(ValueError):
+        obj.name = "Canada"
+
+    with self.assertRaises(ValueError):
+        Model(name="Canada")

docs/source/usage.rst

@@ -45,4 +45,5 @@ For more complex schemas and types see our documentation on
     usage.reference
     usage.allof
     usage.anyof
-    usage.enum
+    usage.enum
+    usage.const