New potential error proposal: piping into eval without operands

There is a common mistake in new users:

``` Bash
echo echo 1 | eval
```

The correct method is:

``` Bash
source <(echo echo 1)
eval "$(echo echo 1)"
```

This is observed at https://unix.stackexchange.com/questions/238582. Some of my friends sometimes make this mistake, too.

This error is serious and almost definite.
