Updated Readme.md

Added info about customizing valid_till_text_size

README.md

@@ -406,6 +406,7 @@ You can modify the dimensions of some of the attributes by adding these attribut
 <dimen name="card_number_text_size">size</dimen>        //Default value:16sp
 <dimen name="card_name_text_size">size</dimen>          //Default value:14sp
 <dimen name="expiry_date_text_size">size</dimen>        //Default value:14sp
+<dimen name="valid_till_text_size">size</dimen>         //Default value:10sp
 <dimen name="brand_logo_width">size</dimen>             //Default value:120dp
 <dimen name="brand_logo_height">size</dimen>            //Default value:40dp
 ```