Wording for verifying HackerNews account is non-obvious

``` bash
keybase prove hackernews
```

> Please edit your HackerNews profile to contain the following text. Click here: […]

… should probably read:

> Please edit your HackerNews profile to contain the following text in the **about** field. Click here: […]

Minimal polish though I had to think for a second here while the other verifications where "literally" no-brainers ;)

Start at the output for `keybase prove hackernews` and locate the text that tells users where to place the verification text. Update it to explicitly name the HackerNews profile's about field, then verify the command presents the clearer wording.

Written by the indexing model from the issue text.