Add MIT license

Open-source under MIT - free for any use including commercial, modify
+ redistribute freely, must preserve the copyright + license notice in
copies, and the standard AS-IS no-warranty / no-liability clauses.

Also sets PackageLicenseExpression=MIT on the project metadata so any
NuGet packages produced from this codebase get the right SPDX tag.

Directory.Build.props

@@ -9,6 +9,7 @@
     <PackageProjectUrl>https://jpaul.me</PackageProjectUrl>
     <RepositoryUrl>https://github.com/recklessop/webhook-server</RepositoryUrl>
     <RepositoryType>git</RepositoryType>
+    <PackageLicenseExpression>MIT</PackageLicenseExpression>
   </PropertyGroup>
 
 </Project>

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2025-2026 Justin Paul
+
+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

@@ -88,4 +88,4 @@ powershell -ExecutionPolicy Bypass -File scripts\build-installer.ps1
 
 ## License
 
-TBD.
+[MIT](LICENSE). Use it for whatever you want, including commercial — just keep the copyright + license notice in copies and don't sue me when it eats your filesystem. No warranty, express or implied.