make it explicit that auth is optional (#69)

* Add basic description to global API meta information

* make it explicit that auth is optional

Auth was added in c077573. Most/All our endpoints are available without
authentication (but some records may be protected) - let's make it
explicit that unauthenticated use is legitimate.

As far as I can tell this has no impact in swagger ui, though.

See
OAI/OpenAPI-Specification#14

specs/openapi.json

@@ -2,7 +2,8 @@
     "openapi":"3.0.2",
     "info": {
         "title":"Wikibase REST API Proposal",
-        "version":"1.0"
+        "version":"1.0",
+        "description": "<p>This is a proposal for the structure of the future Wikibase REST API.</p><h2>Authentication</h2><p>Authentication is optional for all paths but individual resources may require it (e.g. particular items).</p>",
     },
     "servers": [
         { "url":"https://www.wikidata.org/w/rest.php/wikibase/v0" }
@@ -54,6 +55,7 @@
         "$ref": "./paths/index.json"
     },
     "security": [
+        {},
         { "bearerAuth": [] }
     ]
 }