Fix the netstd tutorial console logging and README

In my environment, Client -help doesn't show any help messages before it stops.

thrift/tutorial/netstd$ Client/bin/Debug/netcoreapp3.1/Client -help
thrift/tutorial/netstd$ 

To fix this, disposing the ServiceProvider is required. https://github.com/aspnet/Logging/issues/631

In addition, there are some minor mistakes in README.md. For example:

• (Server|Client) -h doesn't work.
• On Linux, the generated executable names are "Client" and "Server" (camel-cased), not "client" and "server"
• Server's multiplexed protocol is not documented
• Python examples don't address THRIFT-4002