The String#include? method only accepts strings or characters. It does not accept regular expressions.
You can use either of the following to assert against the regexp:
assert(@browser.text.match(/Company employees/))
assert(@browser.text =~ /Company employees/)
assert(@browser.text[/Company employees/])
However, I think it is more clear (reading the code and the error message) if you use the assert_match:
assert_match(/Company employees/, @browser.text)