Merge #9995: [doc] clarify blockchain size and pruning

b26ea0a specify blockchain size & default behaviour (over pruning) (Mike van Rossum)

Tree-SHA512: f21e1ea0df66500f9f899c429984e7c3de6d1cb1a216f2784061731fe22d5b8e9e48042dfc9db3c92adc6d6b6bb0c2578ca431fe5268b2a907ee2c0fdb60b4c5

Author: laanwj

doc/README.md

@@ -3,7 +3,7 @@ Bitcoin Core 0.14.99
 
 Setup
 ---------------------
-Bitcoin Core is the original Bitcoin client and it builds the backbone of the network. However, it downloads and stores the entire history of Bitcoin transactions (which is currently several GBs); depending on the speed of your computer and network connection, the synchronization process can take anywhere from a few hours to a day or more.
+Bitcoin Core is the original Bitcoin client and it builds the backbone of the network. It downloads and, by default, stores the entire history of Bitcoin transactions (which is currently more than 100 GBs); depending on the speed of your computer and network connection, the synchronization process can take anywhere from a few hours to a day or more.
 
 To download Bitcoin Core, visit [bitcoincore.org](https://bitcoincore.org/en/releases/).