added documentation for to, cc, and bcc addressing

doc/hgrc.5.txt

@@ -138,6 +138,13 b' email::'
   from;;
     Optional.  Email address to use in "From" header and SMTP envelope
     of outgoing messages.
+  to;;
+    Optional.  Email address(es) of recipient(s).
+  cc;;
+    Optional.  Email address(es) to send carbon copies to.
+  bcc;;
+    Optional.  Email address(es) to send blind carbon copies to.
+    Cannot be set interactively.
   method;;
     Optional.  Method to use to send email messages.  If value is
     "smtp" (default), use SMTP (see section "[smtp]" for