Update readme

README.md

@@ -18,10 +18,10 @@ $ composer require ksdev/nbp-currency-converter
 
 ## Usage
 
-If you don't pass a table publication date to `convert` or `averageExchangeRates` methods, the last published average 
-exchange rates table will be used, starting from yesterday, so e.g. on 2015-07-10 (friday) a table from 2015-07-09 
-(thursday) will be used, and on 2015-07-12 (sunday) a table from 2015-07-10 (friday) - unless no table was published on 
-this day, then the table from previous day will be used, etc.
+If optional table publication date is not passed to `convert` or `averageExchangeRates` methods, the last published 
+average exchange rates table will be used, starting from yesterday, so e.g. on 2015-07-10 (friday) a table from 
+2015-07-09 (thursday) will be used, and on 2015-07-12 (sunday) a table from 2015-07-10 (friday) - unless no table was 
+published on this day, then the table from previous day will be used, etc.
 
 ``` php
 use Ksdev\NBPCurrencyConverter\CurrencyConverter;