Update benchmark.md

Amend `cd` relative to `polkadot-sdk`, as all the `./target...` executions are relative to the top-level `polkadot-sdk` folder (haven't checked other docs).

content/md/en/docs/test/benchmark.md

@@ -140,7 +140,7 @@ After you have added your pallet, compile your node binary with the `runtime-ben
 For example:
 
 ```bash
-cd bin/node/cli
+cd substrate/bin/node/cli
 cargo build --profile=production --features runtime-benchmarks
 ```