Add README

Author: eemeli

README.md

@@ -0,0 +1,83 @@
+# yaml-to-messageformat
+
+Converts yaml input (e.g. as used by Rails i18n) into [messageformat]-compatible
+JSON.
+
+### Installation
+
+```sh
+npm install yaml-to-messageformat
+```
+or
+```sh
+yarn add yaml-to-messageformat
+```
+
+If using in an environment that does not natively support ES6 features such as
+object destructuring and arrow functions, you'll want to use a transpiler for this.
+
+
+### Usage
+
+```js
+const convert = require('yaml-to-messageformat')
+const { locales, translations } = convert(`
+en:
+  format: "%{attribute} %{message}"
+  errors:
+    confirmation: "doesn't match %{attribute}"
+    accepted: "must be accepted"
+    wrong_length:
+      one: "is the wrong length (should be 1 character)"
+      other: "is the wrong length (should be %{count} characters)"
+    equal_to: "must be equal to %{count}"
+`)
+
+const MessageFormat = require('messageformat')
+const mf = new MessageFormat(locales)
+const messages = mf.compile(translations)
+
+messages.en.errors.accepted()
+// 'must be accepted'
+
+messages.en.format({
+  attribute: 'Problem',
+  message: messages.en.errors.confirmation({ attribute: 'your style' })
+})
+// 'Problem doesn\'t match your style'
+
+messages.en.errors.wrong_length({ count: 42 })
+// 'is the wrong length (should be 42 characters)'
+```
+
+
+### API: `convert(input, options)`
+
+`input` should be a string; `options` is an optional set of configuration for
+the [js-yaml] parser, as well as yaml-to-messageformat itself:
+
+- `filename`, `json`, `onWarning`, `schema` – See the [js-yaml documentation]
+
+- `defaultLocale` (string, default `'en'`) – Sets the initial locale.
+
+- `includeLocales` (array of strings, default `null`) – By default any key in the
+  input data that matches the two-letter code of a [CLDR pluralisation language]
+  switches the language used for determining the pluralisation rules. Set this to
+  some limited set of languages (or even an empty array) to limit that.
+
+- `verbose` (boolean, default `false`) – If set to `true`, some logging and
+  warnings will be printed to the console.
+
+For more options, take a look at the [source](./index.js).
+
+The object returned by the function contains the following fields:
+
+- `locales` (array of strings) – The actual locales encountered in the data
+
+- `translations` (object) – An object containing the MessageFormat strings,
+  matching the shape of the input data
+
+[CLDR pluralisation language]: http://www.unicode.org/cldr/charts/latest/supplemental/language_plural_rules.html
+[messageformat]: https://messageformat.github.io/
+[js-yaml]: https://github.com/nodeca/js-yaml
+[js-yaml documentation]: https://github.com/nodeca/js-yaml#safeload-string---options-