Explain how to publish with --allow-dirty
diff --git a/Cargo.toml b/Cargo.toml
index d1b51f7..ed1840b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -41,4 +41,7 @@
# proc-macro2. Quote would implement its traits for types from that proc-macro2,
# meaning impls would be missing when tested against types from the local
# proc-macro2.
+#
+# When publishing proc-macro2, Cargo will forbid publishing with a patch
+# section. You need to delete this section and then publish with --allow-dirty.
proc-macro2 = { path = "." }