add note about third-party JS, CDNs, and HTTPS

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 6ef0494edcb8a26e618e991d104f7b7c51f9ce5f..7a8a44f2117a875a38b717a26d690358edf2a869 100644 (file)
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -33,6 +33,7 @@ We only accept issues that are bug reports or feature requests. Bugs must be iso
 - Double quotes only, never single quotes
 - Always use proper indentation
 - Use tags and elements appropriate for an HTML5 doctype (e.g., self-closing tags)
+- Use CDNs and HTTPS for third-party JS when possible. We don't use protocol-relative URLs in this case because they break when viewing the page locally via `file://`.
 
 ### CSS