Merge JoinMarket-Org/joinmarket-clientserver#1296: docs: Creating Core wallet is required for v0.21+

4d4cae5f0c docs: Creating Core wallet is required for v0.21+ (Kristaps Kaupe)

Pull request description:

  It isn't anymore "recommended" for recent Bitcoin Core versions, as since v0.21 default wallet is not created automatically.

Top commit has no ACKs.

Tree-SHA512: 617c4af59449926be8873a0af54f4d4dca732862391915578c249f4022369b9dc6c5f3c0201bde1b6e70a8fe301946054d47f78456e092d17a32398ac7cf0013

docs/USAGE.md

@@ -11,7 +11,7 @@ followed a manual installation as per [here](INSTALL.md)).
 
 2. [Configuring for Bitcoin Core](#configure)
 
-   a. [Setting a Core wallet (recommended)](#setting-core-wallet)
+   a. [Setting a Core wallet (required for Bitcoin Core v0.21 and newer)](#setting-core-wallet)
 
 3. [Using the wallet-tool.py script](#wallet-tool)
 
@@ -105,7 +105,9 @@ Note, you can also use a cookie file by setting, in this section, a variable `rp
 
 <a name="setting-core-wallet" />
 
-### Setting a Core wallet (recommended)
+### Setting a Core wallet (required for Bitcoin Core v0.21 and newer)
+
+_NOTE: Although this step is not strictly required for Bitcoin Core versions before 0.21, it is still recommended._
 
 This point often confuses people. Joinmarket has its own wallet, with encryption and storage of keys, separate to Bitcoin Core,
 but it *stores addresses as watch-only in the Bitcoin Core wallet*, and the relevant rpc calls to Bitcon Core always specify the