Add contributing guide for build/test/release

CONTRIBUTING.md

@@ -0,0 +1,45 @@
+# Contributing
+
+Thanks for helping improve Asynkron.Profiler!
+
+## Prerequisites
+
+- .NET SDK 10 preview (see `global.json` for the pinned version).
+
+## Build
+
+From the repo root:
+
+```sh
+dotnet restore
+dotnet build -c Release --nologo
+```
+
+## Test
+
+```sh
+dotnet test -c Release --nologo
+```
+
+## Release
+
+Releases are tag-based and run via GitHub Actions (`.github/workflows/pack.yml`).
+
+1. Create a version tag (example):
+
+```sh
+git tag v1.2.3
+git push origin v1.2.3
+```
+
+2. The workflow packs and publishes:
+   - `src/ProfileTool/ProfileTool.csproj`
+   - `src/ProfilerCore/Asynkron.Profiler.Core.csproj`
+
+If you need to run the pack step locally:
+
+```sh
+VERSION=1.2.3
+dotnet pack -c Release -o ./nupkg src/ProfileTool/ProfileTool.csproj -p:Version="$VERSION"
+dotnet pack -c Release -o ./nupkg src/ProfilerCore/Asynkron.Profiler.Core.csproj -p:Version="$VERSION"
+```