Update 1252.feature.md

changelog.d/1252.feature.md

@@ -5,7 +5,11 @@ can be used multiple times,
 and can be used in parallel with dependencies specified
 through the command line.
 
+Each line is a separate package specifier with the same syntax as the command line.
+Comments are supported with a `#` prefix.
+This is a strict subset of the pip [requirements file format][pip-requirements] syntax.
 
-Note that this is not a full pip-requirements file.
-If you require full pip features, then use the `runpip` command instead;
-although the installed packages won't be recognised as "injected".
+If you require full pip functionality, then use the `runpip` command instead;
+however, the installed packages won't be recognised as "injected".
+
+[pip-requirements]: https://pip.pypa.io/en/stable/reference/requirements-file-format/