Make JWT clearer

Author: benjie

src/postgraphileOptions.js

@@ -1,10 +1,14 @@
 exports.options = {
   dynamicJson: true,
   cors: true,
-  jwtSecret: process.env.JWT_SECRET || String(Math.random()),
   graphiql: false,
   externalUrlBase: '/default',
 
+  // If consuming JWT:
+  jwtSecret: process.env.JWT_SECRET || String(Math.random()),
+  // If generating JWT:
+  jwtPgTypeIdentifier: 'forum_example.jwt_token',
+
   /* If you want to enable GraphiQL, you must use `externalUrlBase` so PostGraphile
    * knows where to tell the browser to find the assets.  Doing this is
    * strongly discouraged, you should use an external GraphQL client instead.