update readme

Author: djih

README.md

@@ -266,6 +266,8 @@ amplitude.getInstance().clearUserProperties();
 
 The preferred method of tracking revenue for a user now is to use `logRevenueV2()` in conjunction with the provided `Revenue` interface. `Revenue` instances will store each revenue transaction and allow you to define several special revenue properties (such as revenueType, productId, etc) that are used in Amplitude dashboard's Revenue tab. You can now also add event properties to the revenue event, via the eventProperties field. These `Revenue` instance objects are then passed into `logRevenueV2` to send as revenue events to Amplitude servers. This allows us to automatically display data relevant to revenue on the Amplitude website, including average revenue per daily active user (ARPDAU), 1, 7, 14, 30, 60, and 90 day revenue, lifetime value (LTV) estimates, and revenue by advertising campaign cohort and daily/weekly/monthly cohorts.
 
+**Important Note**: Amplitude currently does not support currency conversion. All revenue data should be normalized to your currency of choice, before being sent to Amplitude.
+
 Each time a user generates revenue, you create a `Revenue` object and fill out the revenue properties:
 ```javascript
 var revenue = new amplitude.Revenue().setProductId('com.company.productId').setPrice(3.99).setQuantity(3);