Use MIT license and add license file

Author: shumphrey

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) Steven Humphrey
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

@@ -57,8 +57,3 @@ API features require a GitLab instance with v4 of the API.
 > Why doesn't this plugin have a pun name?
 
 I couldn't think of one.
-
-## License
-
-Copyright (c) Steven Humphrey.  Distributed under the same terms as Vim itself.
-See `:help license`.

doc/fugitive-gitlab.txt

@@ -1,7 +1,7 @@
 *fugitive-gitlab.txt*  Gitlab integration for fugitive
 
 Author:  Steven Humphrey <https://github.com/shumphrey>
-License: Same terms as Vim itself (see |license|)
+License: MIT
 
 INTRODUCTION                                    *fugitive-gitlab*