Update the description for persisted-models

Author: Quentin Presley

lib/persisted-model.js

@@ -797,7 +797,9 @@ module.exports = function(registry) {
  accepts: [
  {arg: 'filter', type: 'object', description:
  'Filter defining fields, where, include, order, offset, and limit - must be a ' +
- 'JSON-encoded string ({"something":"value"})'},
+ 'JSON-encoded string ({"where":{"something":"value"}}). ' +
+ 'See https://loopback.io/doc/en/lb3/Querying-data.html#using-stringified-json-in-rest-queries ' +
+ 'for more details.'},
  {arg: 'options', type: 'object', http: 'optionsFromRequest'},
  ],
  returns: {arg: 'data', type: [typeName], root: true},