Update domains.md
Update domains.md

Added blurb for domain WL cap.
ksigler7/docs,Aonepathan/docs,ksigler7/docs,katieporter/docs,hardikjain29/docs,hardikjain29/docs,hardikjain29/docs,Aonepathan/docs,Whatthefoxsays/docs,Zaftula/docs,ksigler7/docs,hardikjain29/docs,katieporter/docs,Aonepathan/docs,Zaftula/docs,sendgrid/docs,katieporter/docs,Zaftula/docs,katieporter/docs,hardikjain29/docs,Whatthefoxsays/docs,katieporter/docs,Aonepathan/docs,Zaftula/docs,Aonepathan/docs,sendgrid/docs,sendgrid/docs,Whatthefoxsays/docs,Zaftula/docs