add new-output handler

doc/riverguile.1

@@ -201,10 +201,35 @@ As of now, river only supports a single seat anyway.
 .RE
 .
 .P
+\fBnew-output\fR
+.RE
+.RS
+A handler installed under this key will be called everytime a new output appears.
+On binding, it is also called for all outputs that already exist at that time.
+.P
+Installing a new-output handler will cause riverguile to run continously.
+.P
+The handler procderure must accept a single argument, the global name of the
+output (integer).
+.P
+Here is an example of a simple new-output handler which merely logs new outputs:
+.P
+.RS
+.EX
+(\fBinstall-handler\fR 'new-output
+  (\fBlambda\fR (output)
+    (\fBdisplay\fR "New output: ")
+    (\fBdisplay\fR output)
+    (\fBnewline\fR)))
+.EE
+.RE
+.RE 
+.
+.P
 \fBexit\fR
 .RE
 .RS
-This key allows you to installs a handler which is called when riverguile exits.
+This key allows you to install a handler which is called when riverguile exits.
 .P
 The procedure takes no arguments.
 .P