KNOWN_BUGS: Add DarwinSSL won't import PKCS#12 without a password

Bug: https://github.com/curl/curl/issues/1308
Reported-by: Justin Clift
diff --git a/docs/KNOWN_BUGS b/docs/KNOWN_BUGS
index 5974821..b438010 100644
--- a/docs/KNOWN_BUGS
+++ b/docs/KNOWN_BUGS
@@ -27,6 +27,7 @@
  2.1 CURLINFO_SSL_VERIFYRESULT has limited support
  2.2 DER in keychain
  2.3 GnuTLS backend skips really long certificate fields
+ 2.4 DarwinSSL won't import PKCS#12 client certificates without a password
 
  3. Email protocols
  3.1 IMAP SEARCH ALL truncated response
@@ -222,6 +223,12 @@
  field is too long in the cert, it'll just return an error and the field will
  be displayed blank.
 
+2.4 DarwinSSL won't import PKCS#12 client certificates without a password
+
+ libcurl calls SecPKCS12Import with the PKCS#12 client certificate, but that
+ function rejects certificates that do not have a password.
+ https://github.com/curl/curl/issues/1308
+
 
 3. Email protocols