add license (#17)

LICENSE

@@ -0,0 +1,29 @@
+PubNub Software Development Kit License Agreement
+Copyright © 2023 PubNub Inc. All rights reserved.
+
+Subject to the terms and conditions of the license, you are hereby granted
+a non-exclusive, worldwide, royalty-free license to (a) copy and modify
+the software in source code or binary form for use with the software services
+and interfaces provided by PubNub, and (b) redistribute unmodified copies
+of the software to third parties. The software may not be incorporated in
+or used to provide any product or service competitive with the products
+and services of PubNub.
+
+The above copyright notice and this license shall be included
+in or with all copies or substantial portions of the software.
+
+This license does not grant you permission to use the trade names, trademarks,
+service marks, or product names of PubNub, except as required for reasonable
+and customary use in describing the origin of the software and reproducing
+the content of this license.
+
+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 PUBNUB OR THE AUTHORS OR COPYRIGHT HOLDERS OF THE SOFTWARE 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.
+
+https://www.pubnub.com/
+https://www.pubnub.com/terms