Add ZapDisable description
Add ZapDisable description

Also, update some of the text, and fix an issue with the useLegacyJit config file syntax.
richlander/dotnet,BruceForstall/dotnet,Microsoft/dotnet,richlander/dotnet,Microsoft/dotnet,punker76/dotnet,velyo/dotnet,BruceForstall/dotnet,velyo/dotnet,690486439/dotnet,punker76/dotnet