docs: Add quotes around $PWD

Author: kroese

.github/readme.md

@@ -33,7 +33,7 @@ services:
 ##### Via Docker CLI:
 
 ```bash
-docker run -it --rm --name rpc-proxy -p 8331:8331 -v ${PWD:-.}/btc_rpc_proxy.toml:/etc/btc_rpc_proxy.toml dobtc/btc-rpc-proxy
+docker run -it --rm --name rpc-proxy -p 8331:8331 -v "${PWD:-.}/btc_rpc_proxy.toml:/etc/btc_rpc_proxy.toml" dobtc/btc-rpc-proxy
 ```
 
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