add webarena in samples (#2114)

* add webarena in samples/tools

* Update samples/tools/webarena/README.md

Co-authored-by: gagb <gagb@users.noreply.github.com>

* Update samples/tools/webarena/README.md

Co-authored-by: gagb <gagb@users.noreply.github.com>

* Update samples/tools/webarena/README.md

Co-authored-by: gagb <gagb@users.noreply.github.com>

* update installation instructions

* black formatting

* Update README.md

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Co-authored-by: gagb <gagb@users.noreply.github.com>
Co-authored-by: Eric Zhu <ekzhu@users.noreply.github.com>