doc: Add security notice for filemd5 and filesha1 functions

website/docs/language/functions/filemd5.mdx

@@ -13,3 +13,8 @@ that hashes the contents of a given file rather than a literal string.
 This is similar to `md5(file(filename))`, but
 because [`file`](/terraform/language/functions/file) accepts only UTF-8 text it cannot be used to
 create hashes for binary files.
+
+Collision attacks have been successfully performed against this hashing
+function. Before using this function for anything security-sensitive, refer to
+[RFC 6151](https://tools.ietf.org/html/rfc6151) for updated security
+considerations applying to the MD5 algorithm.

website/docs/language/functions/filesha1.mdx

@@ -13,3 +13,7 @@ that hashes the contents of a given file rather than a literal string.
 This is similar to `sha1(file(filename))`, but
 because [`file`](/terraform/language/functions/file) accepts only UTF-8 text it cannot be used to
 create hashes for binary files.
+
+Collision attacks have been successfully performed against this hashing
+function. Before using this function for anything security-sensitive, review
+relevant literature to understand the security implications.