Fix base path for grandpa Keys

Author: shekohex

pages/docs/node/systemd.mdx

@@ -193,7 +193,7 @@ rustup target add wasm32-unknown-unknown --toolchain nightly
 
         ```sh filename="Grandpa" copy
 
-        ./target/release/tangle key insert --base-path /data/validator/<USERNAME> \
+        ./target/release/tangle key insert --base-path <BASE_PATH> \
         --chain tangle-testnet \
         --scheme Ed25519 \
         --suri <"12-MNEMONIC-PHARSE"> \