Add source to README table

README.md

@@ -60,6 +60,7 @@ The following price sources are available:
 |Coinbase| `beanprice.coinbase` | [Most common (crypto)currencies](https://api.coinbase.com/v2/exchange-rates) | [Many currencies](https://api.coinbase.com/v2/currencies)| ✓             | ✓                |
 |Coincap | `beanprice.coincap`  | [Most common (crypto)currencies](https://docs.coincap.io)                    | USD                                                      | ✓             | ✓                |
 |Coinmarketcap | `beanprice.coinmarketcap`  | [Most common (crypto)currencies](https://coinmarketcap.com/api/documentation/v1/)| Many Currencies                          | ✓             | ✕                |
+|European Central Bank API| `beanprice.ecbrates`| [Many currencies](https://data.ecb.europa.eu/search-results?searchTerm=exchange%20rates)                     | [Many currencies](https://data.ecb.europa.eu/search-results?searchTerm=exchange%20rates) (Derived from EUR rates)| ✓             | ✓                |
 |IEX     | `beanprice.iex`      | [Trading symbols](https://iextrading.com/trading/eligible-symbols/)          | USD                                                      | ✓             | 🚧 (Not yet!)    |
 |OANDA   | `beanprice.oanda`    | [Many currencies](https://developer.oanda.com/exchange-rates-api/v1/currencies/) | [Many currencies](https://developer.oanda.com/exchange-rates-api/v1/currencies/) | ✓ | ✓ |
 |Quandl  | `beanprice.quandl`   | [Various datasets](https://www.quandl.com/search)                            | [Various datasets](https://www.quandl.com/search)        | ✓             | ✓                |