Document [1] where authors can find it.
[1]: https://github.com/withoutboats/license-exprs/issues/3
# This is an SPDX 2.1 license expression for this package. Currently
# crates.io will validate the license provided against a whitelist of
# known license and exception identifiers from the SPDX license list
-# 2.4.
+# 2.4. Parentheses are not currently supported.
#
# Multiple licenses can be separated with a `/`, although that usage
# is deprecated. Instead, use a license expression with AND and OR
# This is an SPDX 2.1 license expression for this package. Currently
# crates.io will validate the license provided against a whitelist of
# known license and exception identifiers from the SPDX license list
-# 2.4.
+# 2.4. Parentheses are not currently supported.
#
# Multiple licenses can be separated with a `/`, although that usage
# is deprecated. Instead, use a license expression with AND and OR