Update README.md

Co-authored-by: Javier Viola <pepoviola@gmail.com>

README.md

@@ -360,7 +360,7 @@ You can build it from source like this
 
 ```bash
 ❯ git clone git@github.com:paritytech/polkadot-sdk.git
-❯ cd polkadot-sdk/polkadot
+❯ cd polkadot-sdk
 ❯ cargo build --profile testnet -p test-parachain-adder-collator
 ❯ export PATH=$(pwd)/target/testnet:$PATH
 ```