Integrate with FormSpree for submitting 'Contact me' form

To enable the integration, uncomment the section `params.contact.formspree` and set the `formId` value (provided by FormSpree).
It's recommended to change the `btnName` from "Mail me" to "Contact me" as far as visitors won't see your email address.
FormSpree section has preference over `email` if the both are set.

exampleSite/config.yaml

@@ -339,6 +339,9 @@ params:
     # title: "Custom Name"
     content: My inbox is always open. Whether you have a question or just want to say hi, I’ll try my best to get back to you!
     email: [email protected]
+    # formspree:
+    #   enable: true # `contact.email` value will be ignored
+    #   formId: abcdefgh # Take it from your form's endpoint, like 'https://formspree.io/f/abcdefgh'
     btnName: Mail me
 
   footer: