fixes #15340: mention in docs that most selects can't change border-radius
Add woff2 font in readme.md
Merge pull request #15369 from bastienmoulia/woff2

Add woff2 font in readme.md
Add docs for #15340

border-radius CSS property doesn't affect <select>s in some browsers.
Hence, @input-border-radius doesn't affect <select class="form-control"> in some browsers.
Closes #15340.

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Merge branch 'master' of https://github.com/twbs/bootstrap
Merge pull request #15373 from twbs/doc-15340

Add docs for #15340
Port c66e3029df84f55a31f785 over from hosted docs