README.md: fix some typos (ethereum#17381)

Signed-off-by: YaoZengzeng <yaozengzeng@zju.edu.cn>

README.md

@@ -69,7 +69,7 @@ This command will:
  * Start up Geth's built-in interactive [JavaScript console](https://github.com/ethereum/go-ethereum/wiki/JavaScript-Console),
    (via the trailing `console` subcommand) through which you can invoke all official [`web3` methods](https://github.com/ethereum/wiki/wiki/JavaScript-API)
    as well as Geth's own [management APIs](https://github.com/ethereum/go-ethereum/wiki/Management-APIs).
-   This too is optional and if you leave it out you can always attach to an already running Geth instance
+   This tool is optional and if you leave it out you can always attach to an already running Geth instance
    with `geth attach`.
 
 ### Full node on the Ethereum test network