Make the account settings clearer

[ardgedee]

Grant Barrett had a good question in the Slack, basically asking for specifics about what "disable notifications" means: Does it only affect email? (yes, excepting friend requests and group shk invites.) The other settings could also benefit from clarity.

This fix could take several forms: The settings page itself can have more detailed descriptions (which probably wouldn't be a burden since there are only four options), or a section can be added to the FAQ.

[jessamynwest]

I made one small fix just to add email, could probably use a small overhaul but I'd need to poke at CSS to see how to add helper text

[spaceninja]

Helper text can be added to form fields using the field-help class. See the pattern library forms page for an example.

<div class="field">
  <label for="username">Username</label>
  <div class="field-input">
    <input id="username" class="input-text" type="text" value="Your Name">
  </div>
  <div class="field-help">Help text goes here!</div>
</div>