Update _index.en.md

Updated Invalid Selector Exception to note that it can also be caused when inputting an xpath value into an ID-based selector.

Author: Convalytics

website_and_docs/content/documentation/webdriver/troubleshooting/errors/_index.en.md

@@ -15,6 +15,7 @@ aliases: [
 ## Invalid Selector Exception
 
 CSS and XPath Selectors are sometimes difficult to get correct.
+This issue can also arise if you've placed an XPATH value as a parameter to an ID selector. 
 
 ### Likely Cause