Merge #239: docs: fix joinmarket usage instructions

1918af6 docs: fix joinmarket usage instructions (nixbitcoin)

Pull request description:

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Tree-SHA512: a8ad83de8e5e5dfb3670045e001a52f63ef2887b289a6791d8ab998e83d8f5288e01aa187a8e156602189682663edc95abeb8bb4fc3f9a80c487f5c9c89bb10d

Author: jonasnick

docs/usage.md

@@ -245,7 +245,7 @@ you. If however, you want to manually initialize your wallet, follow these steps
 2. Move the automatically generated `wallet.jmdat`
 
     ```console
-    rm /var/lib/joinmarket/wallet.jmdat /var/lib/joinmarket/bak.jmdat
+    mv /var/lib/joinmarket/wallet.jmdat /var/lib/joinmarket/bak.jmdat
     ```
 
 3. Generate wallet on your node