Bundled themes: add README files to explain basic theme usage

[lancewillett]

To match best practices and guidelines for themes in the WordPress.org directory, and to help people get the most of of these themes, we should add README files to each default theme.

The starting content should be based on the Theme Showcase pages from WordPress.com, such as Twenty Fifteen: ​http://theme.wordpress.com/themes/twentyfifteen/.

This came up in discussions at WordCamp London contributor day, with reference to each theme having a changelog file, see #31074.

As noted by mercime in #31074 — we can avoid putting too much textual content into the readme file and instead link to relevant Codex pages. This allows for easier editing (without the need to update the theme itself) and for richer content that has images and links, not just plain text.

First pass at readme.txt files of the Bundled Themes. Attached patches have the following sections in each file:

• Header
• Description
• Installation
• Copyright
• Changelog

The Copyright section also addresses the proper licensing for Bundled themes in #31899

In 32487:

Twenty Fifteen: update readme file.

Props mercime, lancewillett. See #31814.

In 32488:

Twenty Fourteen: add readme file to explain basic theme usage, link to changelog on Codex, and include license information.

See #31814, props mercime.

In 32489:

Twenty Thirteen: add readme file to explain basic theme usage, link to changelog on Codex, and include license information.

See #31814, props mercime.

In 32490:

Twenty Twelve: add readme file to explain basic theme usage, link to changelog on Codex, and include license information.

See #31814, props mercime.

In 32491:

Twenty Eleven: add readme file to explain basic theme usage, link to changelog on Codex, and include license information.

See #31814, props mercime.

In 32492:

Twenty Ten: add readme file to explain basic theme usage, link to changelog on Codex, and include license information.

Closes #31814, props mercime.

In 32493:

Twenty Fifteen: fix typo in readme file, props obenland. Format the release dates as per other bundled themes readme.txt file format.

See #31814.

Is "Tags: " in Description of 2012 intentional?

Replying to TomasM:

Is "Tags: " in Description of 2012 intentional?

Nope! Typo. Good eye. Will fix.

In 32494:

Twenty Twelve: fix typo in readme.txt file.

See #31814, props TomasM.

In 33795:

Twenty Ten: Correct license information in readme.txt.

props Otto42.
see #33590, #31814.

In 33796:

Twenty Eleven: Correct license information in readme.txt.

props Otto42.
see #33590, #31814.

In 33797:

Twenty Twelve: Correct license information in readme.txt.

props Otto42.
see #33590, #31814.

In 33798:

Twenty Thirteen: Correct license information in readme.txt.

props Otto42.
see #33590, #31814.

In 33799:

Twenty Fourteen: Correct license information in readme.txt.

props Otto42.
see #33590, #31814.

In 33800:

Twenty Fifteen: Correct license information in readme.txt.

props Otto42.
see #33590, #31814.