Update TreeSet.md

[hassila]

Fix typo

Replace this paragraph with a description of your changes and rationale. Provide links to an existing issue or external references/discussions, if appropriate.

Checklist

• [ x] I've read the Contribution Guidelines
• [ x] My contributions are licensed under the Swift license.
• [ x] I've followed the coding style of the rest of the project.
• I've added tests covering all new code paths my change adds to the project (if appropriate).
• I've added benchmarks covering new functionality (if appropriate).
• I've verified that my change does not break any existing tests or introduce unexplained benchmark regressions.
• [x ] I've updated the documentation if necessary.

[lorentey]

Good catch! 👍

I think this should better go on release/1.1, not main; would you be willing to rebase this PR on that branch? (Otherwise this change would only show up in the feature release following 1.1.)

[hassila]

Sure, I opened #297 for that, will close this one.

[MaxDesiatov]

Does cherry-picking from release/1.1 to main happen after the fact? If not, should this be reopened and still considered for main?

[lorentey]

I'm manually propagating changes along the release/1.0 → release/1.1 → main chain, so things landing for 1.1 will (eventually) also appear on main -- there is no need to file separate PRs for each branch.

This should probably be explained in the README; I'll make a note to update it.