Update CONTIBUTING.md (#482)

* Update CONTIBUTING.md

* Update CONTIBUTING.md

CONTIBUTING.md

@@ -3,4 +3,30 @@
 One of the easiest ways to contribute is to participate in discussions and discuss issues. You can also contribute by submitting pull requests with code changes.
 
 ## General feedback and discussions?
-Please start a discussion on the [issue tracker](https://github.com/SkyAPM/SkyAPM-dotnet/issues).
+Please start a discussion on the [issue tracker](https://github.com/SkyAPM/SkyAPM-dotnet/issues).
+
+# Build
+
+1. clone this repo
+
+```
+git clone https://github.com/SkyAPM/SkyAPM-dotnet.git
+```
+
+2. Setup Submodule
+
+```
+git submodule update --init
+```
+
+3. build
+```
+// Restore dependencies
+dotnet restore
+// Build Protocol
+dotnet build src/SkyApm.Transport.Grpc.Protocol --no-restore
+// Build
+dotnet build --no-restore
+// Test
+dotnet test --no-build --verbosity normal --framework net6.0
+```