Create a design for a page to allow users to add feeds

[c3ho]

What would you like to be added:
Create a design/mockup for users to add feeds

Why would you like this to be added:
Once #706 and #707 goes in, we need to update Gatsby to use the updated code from those two issues.

[cindyorangis]

This can be broken up into smaller issues:

1. mockup and prototype using Adobe XD
2. implementing the design

Additional information:
This is how we're adding feeds right now https://wiki.cdot.senecacollege.ca/wiki/Planet_CDOT_Feed_List
Let's make adding feeds to Telescope better than this :)

[c3ho]

@cindyledev changed, thanks!

[cindyorangis]

Design mockups were posted here as a comment.

Closing this issue. To be continued in #725.