Clarify relationship to other DB APIs such as IndexedDB

[rvolgers]

The README is very clear on what kind of DB hotspot-db is intending to be, which is great!

While reading it though I realized that it sounded pretty similar to the IndexedDB API available on the web platform. Mainly I'm wondering:

• Is this a coincidence?
• Is there any interest in making an IndexedDB implementation on top of hotspot-db?
• Conversely, is there any interest in implementing the hotspot-db API on top of IndexedDB, for use on the web?