This addresses the remaining nits from #11466
- Updates
doc/files.mdwith respect to the new default wallet directory - Fixes @promag and @laanwj's error message nit, and Jonas' release notes nit
- ~Addresses @laanwj's net-specific wallet subdirectory concern in the case that a walletdir is specified~
- Changes the #includes from "" to <> style after #11651