Merge pull request #872 from krupawan5618/patch-3

Ch 01: Tip Box to address the the discrepancy of exchange rates throughout book

ch01.asciidoc

@@ -214,6 +214,11 @@ In the input field for the bitcoin address, there is a small icon that looks lik
 
 Joe now has Alice's bitcoin address set as the recipient. Joe enters the amount as $10 US dollars and his wallet converts it by accessing the most recent exchange rate from an online service. The exchange rate at the time is $100 US dollars per bitcoin, so $10 US dollars is worth 0.10 bitcoin (BTC), or 100 millibitcoin (mBTC) as shown in the screenshot from Joe's wallet (see <<airbitz-mobile-send>>).
 
+[TIP]
+====
+The price of bitcoin has changed a lot over time, and an incredible amount since the first edition of this book was written. As of March 2021, a person would need approximately $54,000 USD to purchase one whole bitcoin. Many examples in this book reference real-life past transactions, when the price of bitcoin was much lower. Think about how generous of a friend Joe would have been if he had made the same agreement with Alice today!
+====
+
 [[airbitz-mobile-send]]
 [role="smallereighty"]
 .Airbitz mobile bitcoin wallet send screen