add mixed to variant origin docs

Author: acoffman

docs/model/assertions/shared_fields.rst

@@ -20,7 +20,7 @@ Assertions share several fields with evidence, which for the most part can be un
      - :ref:`Molecular Profile Field <evidence-molecular-profile>`
      - 
    * - Origin
-     - :ref:`Gene Field <evidence-gene>`
+     - :ref:`Origin Field <evidence-origin>`
      -
    * - Disease
      - :ref:`Disease Field <evidence-disease>`

docs/model/evidence/origin.rst

@@ -42,6 +42,9 @@ Population frequencies should be based on current population databases (e.g., gn
    * - Combined
      - |attribute-combined|
      - Variants in the corresponding Complex Molecular Profile have heterogeneous origins.
+   * - Mixed
+     - |attribute-mixed|
+     - The population of patient variants described in the Evidence is a mixture of Somatic and Germline.
    * - Unknown
      - |attribute-unknown|
      - The variant origin is uncertain based on the available evidence.