Add pandas logo to repo
- [ ] partially closes #12911
- [x] tests added / passed (N/A)
- [x] passes `git diff upstream/master | flake8 --diff`
- [ ] whatsnew entry

This image has New BSD license, doesn't it? i have set it to cc-by-sa-4.0 [on wikipedia](https://commons.wikimedia.org/wiki/File:Pandas_logo.png)
