Correct example for --form-string

[verhovsky]

$  curl --form-string "data" example.com
Warning: Illegally formatted input field
curl: option --form-string: is badly used here
curl: try 'curl --help' for more information
$  curl --form-string "name=data" example.com
<!doctype html>
<html>
[...]

[bagder]

Thanks!