docs: Update readme for benchmarks (#4181)

test/benchmarks/README.md

@@ -1,15 +1,38 @@
-install google benchmark: https://github.com/google/benchmark
+# VW Benchmarks
 
-by default google benchmark is built in Debug mode so you might want to specify Release mode when building/installing
+## Benchmark results
+Automated benchmarking is performed as part of the VW continuous integration system. Benchmark results are available here: **https://vowpalwabbit.org/vowpal_wabbit/dev/bench/**
 
-build vw benchmarks:
+Benchmarking is done via [github-action-benchmark](https://github.com/benchmark-action/github-action-benchmark).
 
+## Running benchmarks locally
+### C++
+Compile:
 ```
-make -j vw-benchmarks.out
+cmake --preset vcpkg-release -DBUILD_BENCHMARKS=On
+cmake --build build --target vw-benchmarks.out
 ```
 
-run vw benchmarks:
+Run:
+```
+./build/test/benchmarks/vw-benchmarks.out
+```
+
+### .NET
+First, install the VW Nuget packages.
+
+If you want graphs of benchmark results to be automatically generated, make sure that the `RScript` executable is installed and on your PATH.
+```sh
+cd test/benchmarks/dotnet
+
+# Build for both .NET Core and Framework
+dotnet build dotnet_benchmark.csproj --framework net6.0 --runtime win-x64 --configuration Release --no-restore --self-contained
+dotnet build dotnet_benchmark.csproj --framework net4.8 --runtime win-x64 --configuration Release --no-restore --self-contained
+
+# Run with .NET Core as host process
+# Arguments after "--" are for BenchmarkDotNet
+dotnet run --project dotnet_benchmark.csproj --framework net6.0 --runtime win-x64 --configuration Release --no-build -- --filter '*' --join
 
+# Go to output directory
+cd BenchmarkDotNet.Artifacts/results
 ```
-./test/benchmarks/vw-benchmarks.out
-```