Update sources.mdx (#36873)

Highlighted the syntax example (//) next to the plain-text "A special double-slash syntax" for better visibility

Author: dmitryuchuvatov

website/docs/language/modules/sources.mdx

@@ -461,7 +461,7 @@ When the source of a module is a version control repository or archive file
 (generically, a "package"), the module itself may be in a sub-directory relative
 to the root of the package.
 
-A special double-slash syntax is interpreted by Terraform to indicate that
+A special double-slash syntax `//` is interpreted by Terraform to indicate that
 the remaining path after that point is a sub-directory within the package.
 For example: