doc: changed the command used to verify SHASUMS256

Changed the command used to verify with SHASUMS256.txt to another that is simpler and allows you to verify all downloads so you don't have to specify each of them one by one.

README.md

@@ -104,11 +104,10 @@ To download `SHASUMS256.txt` using `curl`:
 curl -O https://nodejs.org/dist/vx.y.z/SHASUMS256.txt
 ```
 
-To check that a downloaded file matches the checksum, run
-it through `sha256sum` with a command such as:
+To check that downloaded files match the checksum, use `sha256sum`:
 
 ```bash
-grep node-vx.y.z.tar.gz SHASUMS256.txt | sha256sum -c -
+sha256sum -c SHASUMS256.txt --ignore-missing
 ```
 
 For Current and LTS, the GPG detached signature of `SHASUMS256.txt` is in