Add README for dotnet examples (#233)

* Add README for dotnet examples
* Remove examples for .NET Core 3.1

examples/dotnet/README.md

@@ -0,0 +1,39 @@
+# .NET Examples
+
+The directory contains examples of how to run Pyroscop to profile .NET applications in Docker containers.
+
+### Fast-slow
+
+The example is a simple single-thread application similar to examples for other spies.
+
+The code is pretty self-explanatory: `Slow.Work` should take 80% of CPU time and remaining 20% to be consumed by
+`Fast.Work`. You may ask why `Fast` and `Slow` classes are defined in separate namespaces. The fact is that Pyroscope
+colors frames depending on the namespaces (for .NET traces), so they are defined in this way just for sake of demo ;)
+
+In this example, the program is built as an executable (`/dotnet/example`), therefore `-spy-name dotnetspy` argument is
+required to tell Pyroscope how to deal with the process:
+> CMD ["pyroscope", "exec", "-spy-name", "dotnetspy", "/dotnet/example"]
+
+To run the example execute the following commands:
+
+```shell
+# cd examples/dotnet/fast-slow
+# docker-compose up
+```
+
+### Web
+
+The example is a simple ASP.NET Core web app that enables you to observe how consumed CPU time is changed by making
+HTTP requests to [http://localhost:5000](http://localhost:5000).
+
+In contrast to the previous example, the application is built as a dynamic library (`/dotnet/example.dll`) and
+runs with dotnet. This allows Pyroscope to automatically detect which kind of spy to use, making `-spy-name` option
+unnecessary:
+> CMD ["pyroscope", "exec", "dotnet", "/dotnet/example.dll"]
+
+To run the example execute the following commands:
+
+```shell
+# cd examples/dotnet/web
+# docker-compose up
+```