Fix my typo introduced months ago and minor change.

Remove the sentence "This is the source" because same README
also is installed with binaries (no source).
So mention developed by ISC.

This was not reviewed.

README

-
-This is the source for Kea, developed by Internet Systems Consortium.
-
 Kea provides DHCPv4 and DHCPv6 servers, a dynamic DNS update module,
 a portable DHCP library, libdhcp++, and a DHCP benchmarking tool,
 perfdhcp.
 
-Th developers website is at http://kea.isc.org/
+Kea is developed by Internet Systems Consortium.
+
+The developers website is at http://kea.isc.org/
 
 Limitations and known issues with this DHCP release can be found
 at http://kea.isc.org/wiki/KeaKnownIssues