Change the example with the "useless use of echo" and backticks

[Strahinja]

One of the examples on the front page,

file=$(echo `basename "$file"`)

is using the deprecated backticks and "useless use of echo". As explainshell.com is likely to be used for learning shell, this potentially teaches those bad habits.

This PR changes the example to

name=$(printf "%s@%s" "$(id -nu)" "$(uname -n)")