Docs On Initializing And Using Bitswap In Readme

[hannahhoward]

It would be great to demonstrate how to setup and use bitswap in the Readme.

This would include initialization:

• creating a libp2p host (can use mocknet for example purposes)
• setting up a bitswap network interface (from Libp2p host -- see network/ipfs_impl.go)
• initializing a blockstore
• creating an instance of bitswap from context, blockstore, and network interface (may want to look at GraphSync README for model for this part) (github.com/ipfs/go-graphsync)

Use Bitswap, Including:

• Request a block with GetBlock
• Request multiple blocks with GetBlocks
• Indicate you have a block with HasBlock
• Get information with WantlistForPeer / LedgerForPeer
• Create a Session (w/ NewSession)
  • GetBlocks from a session

[Stebalien]

This would be awesome!