HOW CAN I ADD OTHER CRYPTOCURRENCIES SUCH AS BITCOIN AS A PAYMENT METHOD USED FOR MY ICO? ERC20 TOKENS ARE THE ONES TO BE PURCHASED.

update**

i am to create an ICO smart contract on the eth network. how do i add bitcoin as a payment method? im having a hard time searching google.

basically the contract gets to receive bitcoin and other alts and in turn the contract executes then sends the erc20 token to a receiving address.