Add an example test for the ":contains()" selector

examples/test_contains_selector.py

@@ -0,0 +1,10 @@
+from seleniumbase import BaseCase
+
+
+class MyTestClass(BaseCase):
+
+    def test_contains_selector(self):
+        self.open("https://xkcd.com/2207/")
+        self.assert_text("Math Work", "#ctitle")
+        self.click('a:contains("Next")')
+        self.assert_text("Drone Fishing", "#ctitle")