Rework "Requesting a package"

[davidjharder]

• A user recently tripped over the old phrasing "Task Tracker"
• Make steps in a sensible order
• Simplify some wording
• Add a brief explanation of allowable licenses with the SPDX list, as this is a common misunderstanding
• Also link the SPDX list in the "Package Inclusion" page

Corresponding PR for the template: https://github.com/getsolus/packages/pull/806