Add MIT license file and support / sponsorship info

.github/FUNDING.yml

@@ -0,0 +1,2 @@
+github: clue
+custom: https://clue.engineering/support

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2013 Christian Lück
+
+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

@@ -18,6 +18,7 @@ implementations.
 
 **Table of contents**
 
+* [Support us](#support-us)
 * [Quickstart example](#quickstart-example)
 * [Usage](#usage)
   * [Factory](#factory)
@@ -27,6 +28,16 @@ implementations.
 * [Install](#install)
 * [License](#license)
 
+## Support us
+
+We invest a lot of time developing, maintaining and updating our awesome
+open-source projects. You can help us sustain this high-quality of our work by
+[becoming a sponsor on GitHub](https://github.com/sponsors/clue). Sponsors get
+numerous benefits in return, see our [sponsoring page](https://github.com/sponsors/clue)
+for details.
+
+Let's take these projects to the next level together! 🚀
+
 ## Quickstart example
 
 ```php
@@ -139,4 +150,7 @@ Its parser and serializer originally used to be based on
 [jpd/redisent](https://github.com/jdp/redisent), which is released under the ISC
 license, copyright (c) 2009-2012 Justin Poliey <[email protected]>.
 
-Other than that, this library is MIT licensed.
+Other than that, this project is released under the permissive [MIT license](LICENSE).
+
+> Did you know that I offer custom development services and issuing invoices for
+  sponsorships of releases and for contributions? Contact me (@clue) for details.