improve IGOFS interface docs (#28)

README.md

@@ -195,19 +195,20 @@ interface IGOFS {
  function rate() external view returns (uint);
 
  // Pin a CID. Value (the GO value for your transaction) must be greater than 0. The GO value you pass in
- // here is how long the file will be pinned for. CID must not be version 0.
+ // here is used to purchase storage for the file at the current rate. The amount of storage purchased
+ // determines how long the file will be pinned for. CID must not be version 0.
  // Emits Pinned events.
  function pin(bytes calldata cid) external payable;
 
- // Get the address of the deposit wallet for a cid. Returns 0x0 if none exists.
+ // Get the address of the wallet for a cid. Returns 0x0 if none exists.
  function wallet(bytes calldata cid) external view returns (address);
 
- // Create a deposit wallet for a cid. Returns false if one already exists. CID must not be version 0.
+ // Create a wallet for a cid. Returns false if one already exists. CID must not be version 0.
  // Emits CreatedWallet events.
  // Uses <=300000 gas.
  function newWallet(bytes calldata cid) external;
 
- // Emitted when a cid is pinned.
+ // Emitted when storage is purchased for a file. bh is amount of storage purchased in byte-hours.
  event Pinned(address indexed user, bytes indexed cid, uint bh);
  // Emitted when a new wallet is created.
  event CreatedWallet(address indexed user, bytes indexed cid, address wallet);