Removed explicit mention of storage requirement (squashed)

Similarly discussed and fixed in the following bitcoin.org issue: bitcoin-dot-org/Bitcoin.org#2716

Removed mention of storage requirement

Agreeing with @laanwj that this mention of the storage requirement could be removed, I did so and changed the wording accordingly.
Would be nice to be able to add a link to a canonical source that is always updated, for those who want a number.

Update doc/README.md

Co-Authored-By: merland <martin@megabit.se>

Update README.md

added a missing 'a'

Author: merland

doc/README.md

@@ -3,7 +3,7 @@ Bitcoin Core
 
 Setup
 ---------------------
-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.
+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 requires a few hundred gigabytes of disk space. 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/).