Describe how to query list of attributes relevant to the category

[krzysztofwolski]

attributes query allows the user to apply inCategory and inCollection filters. This pattern can be used to create dynamic filters for product listings (show attribute filters relevant to the given category).

query AttributesForCategory{
  attributes(filter: {inCategory:"Q2F0ZWdvcnk6MjU="}, first:10, channel: "default-channel"){
    edges{
      node{
        name
        inputType
        choices(first:10){
          edges{
            node{
              name
            }
          }
        }
      }
    }
  }
}

{
  "data": {
    "attributes": {
      "edges": [
        {
          "node": {
            "name": "Medium",
            "inputType": "DROPDOWN",
            "choices": {
              "edges": [
                {
                  "node": {
                    "name": "Vinyl"
                  }
                },
                {
                  "node": {
                    "name": "DVD"
                  }
                },
                {
                  "node": {
                    "name": "VHS"
                  }
                },
                {
                  "node": {
                    "name": "iTunes"
                  }
                },
                {
                  "node": {
                    "name": "CD"
                  }
                },
                {
                  "node": {
                    "name": "MP3"
                  }
                }
              ]
            }
          }
        },
        ...

### Tasks
- [ ] Add examples for `inCategory` filter in the Attribute guide
- [ ] Add link to this guide in the products section

[shubhusion]

kindly assign this issue to me