Add a common license footer for docs

[dewitt]

Confirmed with counsel, and we have a recommended way of communicate the license on docs, including docs which contain inline code samples. In addition to the top-level LICENSE file in the repository containing the text of the Apache License 2.0 (already done), we should add the following footer to each doc:

Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License, and code samples are licensed under the Apache 2.0 License.

In Markdown, just copy the following text verbatim:

Except as otherwise noted, the content of this page is licensed under the
[Creative Commons Attribution 4.0 License](https://creativecommons.org/licenses/by/4.0/),
and code samples are licensed under the
[Apache 2.0 License](https://www.apache.org/licenses/LICENSE-2.0).

[rgregg]

Anyone have a script that makes adding this easier than a copy and paste across 30-40 files?

[dewitt]

for f in **/*.md; do
  cat << EOF >> $f

Except as otherwise noted, the content of this page is licensed under the
[Creative Commons Attribution 4.0 License](https://creativecommons.org/licenses/by/4.0/),
and code samples are licensed under the
[Apache 2.0 License](https://www.apache.org/licenses/LICENSE-2.0).
EOF
done

(Caveat, not tested. )

[rgregg]

Tweaked it slightly, just to add a separator.

for f in **/*.md; do
  cat << EOF >> $f

---

Except as otherwise noted, the content of this page is licensed under the
[Creative Commons Attribution 4.0 License](https://creativecommons.org/licenses/by/4.0/),
and code samples are licensed under the
[Apache 2.0 License](https://www.apache.org/licenses/LICENSE-2.0).
EOF
done