The `cat /tmp/somewhere.txt` command in the example using --dir=$PWD is not needed. The error message should be after the first command anyway since it should be the one creating the message.
It looks like a copy/paste error since the previous example showed the same `cat` command a successful copy.

The error messages appear to have changed since this document was originally written.

…e#6839)
* Docs: Remove unneeded command in WASI-tutorial.md
The `cat /tmp/somewhere.txt` command in the example using --dir=$PWD is not needed. The error message should be after the first command anyway since it should be the one creating the message.
It looks like a copy/paste error since the previous example showed the same `cat` command a successful copy.
* Docs: Update error messages in WASI-tutorial.md.
The error messages appear to have changed since this document was originally written.