Add support for specifying MinimumKeyBits for RSA signatures

man/dkimpy-milter.conf.5

@@ -325,6 +325,13 @@ be set:
 (a) Domain, KeyFile, Selector, no KeyTable, no SigningTable;
 (b) KeyTable, SigningTable, no Domain, no KeyFile, no Selector;
 
+TP
+.I MinimumKeyBits (integer)
+Establishes a minimum key size for acceptable RSA signatures.  Signatures with
+smaller key sizes, even if they otherwise pass DKIM validation, will me marked
+as invalid.  The default is 1024, which accepts all signatures.  A value of
+0 causes the default to be used. Not Applicable to ed25519 signatures.
+
 .TP
 .I OmitHeaders (dataset)
 Specifies a set of header fields that should be omitted when generating