Add volatility text to BAT screen

app/extensions/brave/locales/en-US/preferences.properties

@@ -12,6 +12,7 @@ balance=Balance:
 helloBat=Hello, and thank you for using Brave Payments!
 helloBatText1=Brave Payments allows you to make anonymous, monthly<br>contributions to the publishers you visit on the internet. 
 helloBatText2=Please note that <strong>your Brave Payments Wallet is unidirectional</strong>, and the money you transfer from outside accounts <strong>can not be retrieved or refunded</strong>. The wallet’s primary purpose is to send your contributions to publishers each month, based on your control and advisement.
+helloBatText3=Note: Due to the inherent volatility of cryptocurrency markets, your balance will typically fluctuate on a daily basis.
 batContributionTitle=Introducing BAT Contribution Matching!
 batContributionText1=To say thanks to our early adopters, Brave is matching the next 5.00 USD of BATs that you add to your wallet.
 batContributionText2=Just transfer any amount from your crypto-currency wallet and we’ll match the next 5.00 USD.

app/renderer/components/preferences/payment/addFundsDialog/steps/addFundsBatScreen.js

@@ -24,6 +24,9 @@ class BatWelcomeScreen extends React.Component {
         <p data-l10n-id='helloBatText2'
           className={css(styles.batScreen__text)}
         />
+        <p data-l10n-id='helloBatText3'
+          className={css(styles.batScreen__text)}
+        />
       </div>
     )
   }