Soshelp does not show available switches

When working with sosplugin in lldb, neither `soshelp` nor `help <sos-command>` display available switches. e.g. `help clrstack` could indicate that `-f` shows stacks from all frames (option which is also missing in [docs](https://docs.microsoft.com/en-us/dotnet/framework/tools/sos-dll-sos-debugging-extension#commands)), `-a` is a composite fo `-l` and `-p` etc.