Add comments to on chain market maker

examples/market_maker/on_chain_market_maker.v.py

@@ -1,9 +1,13 @@
 total_eth_qty: public(wei_value)
 total_token_qty: public(currency_value)
+# Constant set in `initiate` that's used to calculate
+# the amount of ether/tokens that are exchanged
 invariant: public(num(wei * currency))
 token_address: address(ERC20)
 owner: public(address)
 
+# Sets the on chain market maker with its owner, intial token quantity,
+# and initial ether quantity
 @public
 @payable
 def initiate(token_addr: address, token_quantity: currency_value):
@@ -16,6 +20,7 @@ def initiate(token_addr: address, token_quantity: currency_value):
     self.invariant = msg.value * token_quantity
     assert self.invariant > 0
 
+# Sells ether to the contract in exchange for tokens (minus a fee)
 @public
 @payable
 def eth_to_tokens():
@@ -28,6 +33,7 @@ def eth_to_tokens():
     self.total_eth_qty = new_total_eth
     self.total_token_qty = new_total_tokens
 
+# Sells tokens to the contract in exchange for ether
 @public
 def tokens_to_eth(sell_quantity: currency_value):
     self.token_address.transferFrom(msg.sender, self, as_num256(sell_quantity))
@@ -38,6 +44,7 @@ def tokens_to_eth(sell_quantity: currency_value):
     self.total_eth_qty = new_total_eth
     self.total_token_qty = new_total_tokens
 
+# Owner can withdraw their funds and destroy the market maker
 @public
 def owner_withdraw():
     assert self.owner == msg.sender