Documenting cat with an example in Apiary

[RichardLitt]

I'm unsure how to document this adequately.

$ curl -i http://localhost:5001/api/v0/cat?arg=QmeomffUNfmQy76CQGy9NdmqEnnHU9soCexBnGU3ezPHVH

HTTP/1.1 200 OK
Content-Length: 5
Transfer-Encoding: chunked
X-Stream-Output: 1

test

What is the output of a cat command? What is the mime-type of a chunked file? I don't know, and I'm having difficulty googling it.

Further, cat shouldn't return both content-length and transfer-encoding. See ipfs/kubo#1776 for more on that.

[RichardLitt]

Maybe we should the same thing as in ipfs block:

## get [GET /block/get{?arg}]

Store data as a raw ipfs block.

+ Parameters
    + arg (Multihash, required) - hash of the block to be fetched

+ Response 200 (text/plain)

    + Body

        ```
        hello world
        ```

Block doesn't always have a plain text mimetype, does it? Does cat?