Add LICENSE file

[julien-deramond]

Closes #338

This PR suggests to add a LICENSE file to fix #338 and so that this repo has an official license.

[mdo]

Maybe we should just remove this line for the blog?

[julien-deramond]

Oh I didn't see what's mentioned in the README file:

All content within src/content/posts/ is copyright Bootstrap. Do not reuse any part without written permission.

We could add a specific section to this LICENSE file to mention that src/content/posts is CC by 3.0:

---

Creative Commons Licensed Directory

src/content/posts is licensed under a Creative Commons Attribution 3.0 Unported License.
To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/.

Or any other stricter license.

Note: It is not done in our main repo even if the "docs" is considered as Creative Commons 3.0.

[XhmikosR]

@julien-deramond I agree with your suggestion. Let's mention both cases in LICENSE and land this :)

[julien-deramond]

Done by adding the following content:

-----------------------------------------------------------------------------

Directory 'src/content/posts' is licensed under the Creative Commons
Attribution 3.0 Unported License.

This work is licensed under the Creative Commons Attribution 3.0 Unported
License. To view a copy of this license, visit
http://creativecommons.org/licenses/by/3.0/.