Add copyright to debian folder (#231)

Reasoning: The copyrights will be included the debian packages and can be scanned on a deployed VM by Delphix's automation.

Author: sravyamks

debian/copyright

@@ -0,0 +1,23 @@
+Format: http://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
+Upstream-Name: sdb
+Source: https://github.com/delphix/sdb
+
+Files: *
+Copyright: Delphix Corp.
+License: Apache-2.0
+
+License: Apache-2.0
+ Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+ You may obtain a copy of the License at
+ .
+     http://www.apache.org/licenses/LICENSE-2.0
+ .
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+ .
+ On Debian systems, the complete text of the Apache License can be found in
+ the file `/usr/share/common-licenses/Apache-2.0'.