Note slapd map type for internal searches

doc/man/man5/slapo-rwm.5

@@ -427,8 +427,8 @@ This limit is overridden by setting specific per-rule limits
 with the `M{n}' flag.
 
 .SH "MAPS"
-Currently, few maps are builtin and there are no provisions for developers
-to register new map types at runtime.
+Currently, few maps are builtin but additional map types may be
+registered at runtime.
 
 Supported maps are:
 .TP
@@ -470,6 +470,20 @@ The parameter
 can be 2 or 3 to indicate the protocol version that must be used.
 The default is 3.
 
+.TP
+.B slapd <URI>
+The
+.B slapd
+map expands a value by performing an internal LDAP search.
+Its configuration is based on a mandatory URI, which must begin with
+.B "ldap:///"
+(i.e., it must be an LDAP URI and it must not specify a host).
+As with the
+LDAP map, the
+.B attrs
+portion must contain exactly one attribute, and if
+a multi-valued attribute is used, only the first value is considered.
+
 .SH "REWRITE CONFIGURATION EXAMPLES"
 .nf
 # set to `off' to disable rewriting