docs: Add error samples

src/error/ErrorUtil.ts

@@ -8,6 +8,18 @@ export function gotRateLimited(error: AxiosError): boolean {
   return error.response?.status === 429;
 }
 
+/**
+ * Possible errors returned from Coinbase Pro API:
+ * { message: 'size is too accurate. Smallest unit is 0.00000001' }
+ * { message: 'size is too small. Minimum size is 0.10000000' }
+ * { message: 'Insufficient funds' }
+ * { message: 'NotFound' }
+ *
+ * Error handling in the official API client:
+ * https://github.com/coinbase/coinbase-pro-trading-toolkit/blob/e95c76eb43bda1fd86379612644a79b02948c17a/src/core/Trader.ts#L122-L126
+ *
+ * @param error Error response wrapped by "axios" request library
+ */
 export function getErrorMessage(error: AxiosError): string {
   const responseWithErrorMessage = error as AxiosError<{message: string}>;
   return responseWithErrorMessage.response?.data.message || error.message;