docs: add sidebar for wiki

Author: spwoodcock

docs/_Sidebar.md

@@ -0,0 +1,17 @@
+# [Home](https://github.com/hotosm/osm-fieldwork/wiki)
+
+[About](https://github.com/hotosm/osm-fieldwork/wiki/about)
+
+[Postgres](https://github.com/hotosm/osm-fieldwork/wiki/postgres)
+
+[YAML](https://github.com/hotosm/osm-fieldwork/wiki/yaml)
+
+[JSON](https://github.com/hotosm/osm-fieldwork/wiki/json)
+
+[Importer](https://github.com/hotosm/osm-fieldwork/wiki/importer)
+
+[Overture](https://github.com/hotosm/osm-fieldwork/wiki/overture)
+
+[Geofabrik](https://github.com/hotosm/osm-fieldwork/wiki/geofabrik)
+
+[API](https://github.com/hotosm/osm-fieldwork/wiki/api)