Add a snippet for Mad Hatter durability recommendations

For Mad Hatter durability operations, we are recommending applications:

• Increase kvEndpoints to 16 (caveated that this should be adjusted as appropriate for the user's environment)
• Increase the default reader and writer threads.
• There's a new default timeout for durable ops in SDK3.  We don't necessarily need to tell users this, as the point of doing it in code was that it would 'just work' without the user needing to make any changes.  TBD whether we mention it.