Publish some benchmarks

When searching for different python time libraries there still countless articles popping up who suggest that especially pendulum has a huge speed advantage over arrow.
While these might have been true, it's absolutely unclear how the situation has changed since then.
It would be nice if there was a small benchmark section in the docs which would compare basic operations.

No files or tests are named. Start by locating the documentation structure and reviewing how existing examples or comparisons are presented; identify basic operations to compare for Arrow and Pendulum. Done means a small benchmark section is published in the docs and clearly reports the current results.

Written by the indexing model from the issue text.