website: Minor updates to learning part3 cache intro

Changed the name of the folder in the Sconsopts link
Current name: MSI_protocol. Matches with gem5 dir

Corrected the spelling for excerpt.

Change-Id: I108765805b3f4b06287bbe3d172f632da6e586ce
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/60810
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby Bruce <bbruce@ucdavis.edu>
Reviewed-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
1 file changed