Document the pattern/purpose of naming conventions for structs 

While using the Java/Kotlin bindings I noticed we have a number of "weirdly" named structs e.g `Result_InvoiceNoneZ` `Result_NoneChannelMonitorUpdateErrZ`, `Option_C2Tuple_usizeTransactionZZ` and `Result_NetworkGraphDecodeErrorZ`. I imagine this is something to do with how our bindings are generated using Rust, but worth addressing since the syntax is a lot different stylistically. 