docs: update instructions for debugging LSP
Previously, it was suggested to set:
vim.lsp.log.set_format_func(vim.inspect)
This made sense before f72c13341a, when
`format_func` was called once per argument being logged, but since that
commit it's called with the log level followed by the other args, so the
suggested setting would call `vim.inspect(log_level, ....)` which would
just print the human readable name of the current log level and no other
details, for example with this set I saw in my logs:
"DEBUG""DEBUG""DEBUG""DEBUG"
Instead just rely on the default formatter, which will:
> ... log the level, date, source and line number of the
caller, followed by the arguments.
578727c25e