Squashed 'third_party/apriltag/' content from commit 3e8e974d0

git-subtree-dir: third_party/apriltag
git-subtree-split: 3e8e974d0d8d6ab318abf56d87506d15d7f2cc35
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
Change-Id: I04ba3cb2106b6813a1013d57aa8074c26f856598
diff --git a/example/README b/example/README
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+These example programs are meant for distribution, and thus will not build in the april2 tree without modifications.