Missing Windows System Statistics input plugin doc

[eschabell]

Missing WINSTAT input plugin doc for this code https://github.com/fluent/fluent-bit/blob/master/plugins/in_winstat/winstat.c

Also need to update Summary.md file with file name windows-system-statistics.md. Note I need a windows machine to test and explore this.

[eschabell]

@esmerel would you like to take a look at the linked PR for a post-review?