Update POST request description

@danrschlosser 

The sample code uses a POST request, but describes a GET request. Made the minor correction.

Though it doesn't matter for the purposes of this tutorial, if we were being pedantic, for a feature like search, GET is preferable because it's idempotent. Search only retrieves data, it doesn't change anything on the server side. It doesn't really matter if we teach them good practices at this stage, since I assume the purpose of this section is to just show them how POST requests work.