Add changelog and release schedule (#99)

Divide the changelog into - Language updates, PHP and Node.js section

PHP and Node.js changelog will list library related changes and will
reuse Language updates section.

Bug: T218639
Co-authored-by: Niklas Laxström <niklas.laxstrom@gmail.com>

CHANGELOG.md

@@ -0,0 +1,31 @@
+# Changelog
+
+Documentation can be found [here](https://language-data.readthedocs.io/en/latest/). Changelog is divided into the following,
+
+- [Language updates](#language-updates)
+- [PHP](#php)
+- [Node.js](#nodejs)
+
+## Language updates
+### 2020-05-20
+Language data related changes,
+1. [Add shy-latn and szy](https://github.com/wikimedia/language-data/pull/76)
+2. [Add Chukchi (ckt)](https://github.com/wikimedia/language-data/pull/78)
+3. [Fix autonym for Kildin Sami (sjd)](https://github.com/wikimedia/language-data/pull/90)
+4. [Change spelling of Innu-aimun autonym](https://github.com/wikimedia/language-data/pull/93)
+5. [Add Sylheti ](https://github.com/wikimedia/language-data/pull/94)
+6. [Split ary to ary-latn and ary-arab](https://github.com/wikimedia/language-data/pull/92)
+7. [Add Middle East and Africa to relevant Arabic varieties](https://github.com/wikimedia/language-data/pull/92)
+8. [Add Mongolian in vertical script ](https://github.com/wikimedia/language-data/pull/95)
+9. [Add AM as a region for Venetian](https://github.com/wikimedia/language-data/pull/96)
+
+## PHP
+### PHP 1.0.0 (2020-05-20)
+- See [language updates 2020-05-20](#2020-05-20).
+- Add PHP support. [Documentation](https://language-data.readthedocs.io/en/latest/api/languagedata/languageutil.html). [Packagist](https://packagist.org/packages/wikimedia/language-data).
+
+## Node.js
+### Node.js 0.2.0 (2020-05-20)
+- See [language updates 2020-05-20](#2020-05-20).
+- Fix `npm audit` warnings.
+- Update minimum supported Node.js version to 8.0.0.