Add examples from 'Personalizations Example Index' to USE_CASES.md
Add examples from 'Personalizations Example Index' to USE_CASES.md

karmakaze/sendgrid-go,sendgrid/sendgrid-go,VividCortex/sendgrid-go,VividCortex/sendgrid-go,sendgrid/sendgrid-go,karmakaze/sendgrid-go