meta: update LICENSE

Port over LICENSE from the radicle-link repository, while also adding
a copyright for Radicle Git Contributors for any further additions to
this repository.

Signed-off-by: Fintan Halpenny <fintan.halpenny@gmail.com>

LICENSE

@@ -1,4 +1,22 @@
-                    GNU GENERAL PUBLIC LICENSE
+radicle-git
+Copyright © 2019-2021 The Radicle Foundation <hello@radicle.foundation>
+Copyright © 2021-2022 The Radicle Link Contributors
+<https://github.com/radicle-dev/radicle-link/graphs/contributors>
+Copyright © 2022 The Radicle Git Contributors
+<https://github.com/radicle-dev/radicle-git/graphs/contributors>
+
+radicle-link is licensed under version 3 of the GNU General Public License
+(GPLv3). Any contribution to radicle-link must be made subject to the
+Developer Certificate of Origin (DCO).
+
+By making your contribution, you are making the declaration set out in the
+Linux Foundation’s Developer Certificate of Origin version 1.1, in which
+the “open source licence indicated in the file” is GPLv3. A copy of the
+DCO can be found in the file named “DCO”.
+
+--------------------------------------------------------------------------
+
+                      GNU GENERAL PUBLIC LICENSE
                        Version 3, 29 June 2007
 
  Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
@@ -619,56 +637,3 @@ Program, unless a warranty or assumption of liability accompanies a
 copy of the Program in return for a fee.
 
                      END OF TERMS AND CONDITIONS
-
-            How to Apply These Terms to Your New Programs
-
-  If you develop a new program, and you want it to be of the greatest
-possible use to the public, the best way to achieve this is to make it
-free software which everyone can redistribute and change under these terms.
-
-  To do so, attach the following notices to the program.  It is safest
-to attach them to the start of each source file to most effectively
-state the exclusion of warranty; and each file should have at least
-the "copyright" line and a pointer to where the full notice is found.
-
-    <one line to give the program's name and a brief idea of what it does.>
-    Copyright (C) <year>  <name of author>
-
-    This program is free software: you can redistribute it and/or modify
-    it under the terms of the GNU General Public License as published by
-    the Free Software Foundation, either version 3 of the License, or
-    (at your option) any later version.
-
-    This program is distributed in the hope that it will be useful,
-    but WITHOUT ANY WARRANTY; without even the implied warranty of
-    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-    GNU General Public License for more details.
-
-    You should have received a copy of the GNU General Public License
-    along with this program.  If not, see <https://www.gnu.org/licenses/>.
-
-Also add information on how to contact you by electronic and paper mail.
-
-  If the program does terminal interaction, make it output a short
-notice like this when it starts in an interactive mode:
-
-    <program>  Copyright (C) <year>  <name of author>
-    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
-    This is free software, and you are welcome to redistribute it
-    under certain conditions; type `show c' for details.
-
-The hypothetical commands `show w' and `show c' should show the appropriate
-parts of the General Public License.  Of course, your program's commands
-might be different; for a GUI interface, you would use an "about box".
-
-  You should also get your employer (if you work as a programmer) or school,
-if any, to sign a "copyright disclaimer" for the program, if necessary.
-For more information on this, and how to apply and follow the GNU GPL, see
-<https://www.gnu.org/licenses/>.
-
-  The GNU General Public License does not permit incorporating your program
-into proprietary programs.  If your program is a subroutine library, you
-may consider it more useful to permit linking proprietary applications with
-the library.  If this is what you want to do, use the GNU Lesser General
-Public License instead of this License.  But first, please read
-<https://www.gnu.org/licenses/why-not-lgpl.html>.