Go Dev wiki has other things that are not in here

[StevenACoffman]

I noticed that there's a lot of stuff in https://go.dev/wiki/Resources-for-slog that are not in this repo, and vice versa.

For instance, this page has no testing utilities such as:

• slogassert - slog handler for testing slog code logs expected results
• slogt- Bridge between Go testing.T and slog

[sagikazarmark]

@StevenACoffman feel free to add a testing utilities category with those libraries.

[sagikazarmark]

Added some of those utilities. Feel free to add more.