make operation parameter "schema" property easier to understand

[chrisckchang]

It's not clear that "who" is actually of type Operation Parameter- the user may be left wondering why schema: { type: 'string' } is used as opposed to type: 'string'.

get: {
          parameters: { 
            who: {
              location: 'query',
              required: false,
              default: 'world',
              schema: { type: 'string' }
            }
          }

Maybe we can do an example where the operation parameter consists of multiple properties? Or improve documentation around this.