Copyright for golang-golang-x-xerrors source package in Focal

Format: https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
Upstream-Name: xerrors
Source: https://github.com/golang/xerrors

Files: *
Copyright: 2019 The Go Authors
License: BSD-3-clause

Files: debian/*
Copyright: 2019 Thorsten Alteholz 
License: BSD-3-clause
Comment: Debian packaging is licensed under the same terms as upstream

License: BSD-3-clause
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions are
 met:
 .
    * Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above
      copyright notice, this list of conditions and the following disclaimer
      in the documentation and/or other materials provided with the
      distribution.
    * Neither the name of Google Inc. nor the names of its
      contributors may be used to endorse or promote products derived from
      this software without specific prior written permission.
 .
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 A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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