Put file and size constraints on what files can be added to meme editor

[0xjim]

SVG GIF (up to 1MB?) PNG JPEG JPG

Not allowed

• mp4
• pdf

[0xjim]

Need Design to figure out where the copy should live.

[diegoprudencios]

Added a copy below the buttons. The default state is black, and if users try to upload something not supported, it turns bold and red.

Here: https://www.figma.com/file/wXczUcc9WlLtpuVJmHVYZm/Memixer---Fixes-1?node-id=1701%3A18928