UI improvements for independent use

[terichadbourne]

This tool is awesome! It was a great visual tool during the IPFS Camp course on the Lifecycle of Data in DWeb, where there was opportunity to narrate over its use. To make it more useful independently, I'd suggest a few tweaks to compensate for the lack of that voice-over:

• Spell out GC as garbage collection
• Add a key to explain color coding
• Note that you drag files onto it to get started
• Add instructions on how to pin something (if that’s an option)