Enhance Preferences Roles UX

[brownhoward]

Based on comments on SolidOS/userguide#17.

User Story

As a Data Browser user, I want to clearly understand the use of Roles within the Data Browser and how to select them, so I can access advanced Data Browser functionality.

Acceptance Criteria

1. The Roles section of the Preferences page displays:
   a. A short description about Roles and their use within the Data Browser.
   b. A tip on how to select multiple roles.
2. The Userguide is updated to reflect the enhancement.

Dev Notes

• Use fieldset to group the roles with legend "Roles".
• Potentially use input=checkbox + label=for (instead of option) per role. Easy to select a role at a time, and for multiple role selections, it doesn't require key or click combinations.
• Reuse text from userguide#roles for the short description of a role either after each label or have a title (for tooltip) or some other indicator to help find out about the capabilities.