Give some hint about the signature of CRL.export in the docstring
diff --git a/src/crypto/crl.c b/src/crypto/crl.c
index 025df50..fa6ae86 100644
--- a/src/crypto/crl.c
+++ b/src/crypto/crl.c
@@ -110,7 +110,7 @@
 }
 
 static char crypto_CRL_export_doc[] = "\n\
-Export a CRL as a string\n\
+export(cert, key[, type[, days]]) -> export a CRL as a string\n\
 \n\
 @param cert: Used to sign CRL.\n\
 @type cert: L{X509}\n\