[Miscellaneous] Add License (mettle#7)

* Create LICENSE

* Add license to composer.

Author: dljfield

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2020 Mettle
+
+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.

composer.json

@@ -2,6 +2,7 @@
     "name": "mettle/sendportal",
     "type": "project",
     "description": "SendPortal. Open-source self-hosted email marketing. Manage your own newsletters at a fraction of the cost.",
+    "license": "MIT",
     "require": {
         "php": "^7.2.5",
         "fideloper/proxy": "^4.2",