SkQP: branching tools updated.

1.  get_gold_export_url.py becomes get_gold_results.py

2.  README_GENERATING_MODELS.md updated with changed and more
    complete instructions.

No-Try: true
Change-Id: I7fb84ad99e3049717ea9a572f8558ed2f73d412c
Reviewed-on: https://skia-review.googlesource.com/c/184600
Reviewed-by: Hal Canary <halcanary@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
2 files changed