[2.7] bpo-33943: Add references in the docs for logging.basicConfig (GH-7858) (GH-7902)

Adds references to info about file modes, `time.strftime()`, string formatting
syntaxes, and logging levels.

(cherry picked from commit a8ddf85a84364d2c660e6670a7e06621993d1fdc)

Co-authored-by: Andrés Delfino <adelfino@gmail.com>
1 file changed