[jreed-host] improve README

Don't document b10-host in README, since now have manual page.

src/bin/host/README

@@ -1,14 +1,4 @@
-Rewriting host(1) in C++ from scratch using BIND 10's libdns.
+Rewriting host(1) in C++ from scratch using BIND 10's libdns++.
 
-Initial functionality:
-
-  host _hostname_ [server]
-
-By default, it looks up the A, AAAA, and MX record sets.
-
-Note it doesn't use /etc/resolv.conf at this time.
-The default name server used is 127.0.0.1.
-
-  -r	 	disable recursive processing
-  -t _type_	specific query type 
-  -v		enable verbose output mode, including elapsed time
+The bugs and incompatibilities are listed in the manual page
+and in the source code.