Add examples in help

[jimaek]

add examples under every command help

perfops --help
perfops ping --help
...

[boki]

@jimaek Won't it get a bit too much text to add examples to perfops --help?

[jimaek]

Not all of them, just 1 to show how the command works.

For example:

e.g perfops ping google.com --from Europe --limit 2

[boki]

Oh: should the examples include output or not, e.g., just show the command?

[jimaek]

no output, just the command example