docs: Add LICENSE and README

Author: eemeli

LICENSE

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+Copyright Eemeli Aro <eemeli@gmail.com>
+
+Permission to use, copy, modify, and/or distribute this software for any purpose
+with or without fee is hereby granted, provided that the above copyright notice
+and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
+THIS SOFTWARE.

README.md

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+# yaml-types
+
+Additional useful types for [`yaml`](https://github.com/eemeli/yaml).
+
+## Installation and Usage
+
+```
+npm install yaml yaml-types
+```
+
+Each type (a.k.a. "tag") is available as a named export of `'yaml-types'`.
+These may then be used as [custom tags](https://eemeli.org/yaml/#writing-custom-tags):
+
+```js
+import { parse } from 'yaml'
+import { regexp } from 'yaml-types'
+
+const re = parse('!re /fo./g', { customTags: [regexp] })
+'foxbarfoo'.match(re) // [ 'fox', 'foo' ]
+```
+
+## Available Types
+
+- `regexp` (`!re`) - [RegExp] values,
+  using their default `/foo/flags` string representation.
+
+[RegExp]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_expressions
+
+## Customising Tag Names
+
+To use one of the types with a different tag identifier, set its `tag` value accordingly.
+For example, to extend the default namespace with `!!js/regexp` instead of using a locale `!re` tag for RegExp values:
+
+```js
+import { stringify } from 'yaml'
+import { regexp } from 'yaml-types'
+
+const myregexp = { ...regexp, tag: 'tag:yaml.org,2002:js/regexp' }
+const str = stringify(/fo./m, { customTags: [myregexp] })
+// '!!js/regexp /fo./m\n'
+```
+
+## Contributing
+
+Additions to this library are very welcome!
+Many data types are useful beyond any single project,
+and while the core `yaml` library is mostly limited to the YAML spec,
+no such restriction applies here.
+
+The source code is written in [TypeScript], and the tests use [Node-Tap].
+When submitting a PR for a new type, tests and documentation are required,
+as well as satisfying [Prettier].
+
+[TypeScript]: https://www.typescriptlang.org/
+[Node-Tap]: https://node-tap.org/
+[Prettier]: https://prettier.io/