Add link to VERSIONS file format

Author: sharkdp

crates/red_knot_test/src/parser.rs

@@ -133,13 +133,17 @@ struct EmbeddedFileId;
 
 /// A single file embedded in a [`Section`] as a fenced code block.
 ///
-/// Currently must be a Python file (`py` language), a type stub (`pyi`) or a `VERSIONS` file.
+/// Currently must be a Python file (`py` language), a type stub (`pyi`) or a [typeshed `VERSIONS`]
+/// file.
+///
 /// TOML configuration blocks are also supported, but are not stored as `EmbeddedFile`s. In the
 /// future we plan to support `pth` files as well.
 ///
 /// A Python embedded file makes its containing [`Section`] into a [`MarkdownTest`], and will be
 /// type-checked and searched for inline-comment assertions to match against the diagnostics from
 /// type checking.
+///
+/// [typeshed `VERSIONS`]: https://github.com/python/typeshed/blob/c546278aae47de0b2b664973da4edb613400f6ce/stdlib/VERSIONS#L1-L18
 #[derive(Debug)]
 pub(crate) struct EmbeddedFile<'s> {
     section: SectionId,