sweet: ignore config file and results directory

Change-Id: Id5d05cabd415c6b445273209259246d0b16439e4
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/445135
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>