document "common_query" config options (#143)

ovos_config/mycroft.conf

@@ -167,6 +167,18 @@
       "single_thread": true
     },
 
+    // Common Query gathers responses to questions from various skills and chooses the best answer
+    "common_query": {
+      // maximum seconds to wait for skill responses before giving up
+      "max_response_wait": 6,
+      // how much extra seconds to allow a skill to search if it requests so
+      "extension_time": 3,
+      // reranker plugins are responsible for selecting the best answer among skill responses in case of ties
+      // the default is a BM25 implementation from ovos-classifiers
+      "reranker": "ovos-choice-solver-bm25"
+    },
+
+    // OVOS Common Play - handle media requests
     "OCP": {
       // enable usage of a pretrained classifier for MediaType matching
       // if disabled a simple .voc match is used