Add documentation to tell users how to create a Scorch fts index

Hi Amarantha,

As you know, Scorch is a new fts index scheme all set to 'DP' in Vulcan, performs better than the default up-side-down index in some cases, esp Windows. We need to educate the users on how to create a scorch index. Can you please add documentation for the same?

One can create a 'Scorch' fts index by passing "indexType": "scorch" under "store" in the index definition like -

{

  "params": {

    "store": {

      "kvStoreName": "mossStore",

      "indexType": "scorch"

    }

  },

  "name": "default_index_1",

  "planParams": {

    "numReplicas": 0,

    "maxPartitionsPerPIndex": 171

  },

  "sourceName": "default",

  "sourceUUID": "",

  "sourceType": "couchbase",

  "type": "fulltext-index",

  "uuid": ""

}

Thanks
Aruna