Should I add Guest Lecturer experience in my CV?
I've seen a lot of CVs include guest lecturer. You would include it in the Teaching section of your CV.  A quick google for "guest lecturer cv" will show you some examples. 

Do note, this is generally different than an invited speaker though. A Guest Lecturer comes and teaches a class where as an Invited Speaker comes to give a talk or seminar or colloquium. If this is an invited talk then you'd still list it on your CV, but in the Invited Talks section.