[readme] rename, add badges

README.md

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+# concat-map <sup>[![Version Badge][npm-version-svg]][package-url]</sup>
+
+[![github actions][actions-image]][actions-url]
+[![coverage][codecov-image]][codecov-url]
+[![License][license-image]][license-url]
+[![Downloads][downloads-image]][downloads-url]
+
+[![npm badge][npm-badge-png]][package-url]
+
+Concatenative mapdashery.
+
+## example
+
+``` js
+var concatMap = require('concat-map');
+var xs = [ 1, 2, 3, 4, 5, 6 ];
+var ys = concatMap(xs, function (x) {
+    return x % 2 ? [ x - 0.1, x, x + 0.1 ] : [];
+});
+console.dir(ys);
+```
+
+
+```js
+[ 0.9, 1, 1.1, 2.9, 3, 3.1, 4.9, 5, 5.1 ]
+```
+
+## methods
+
+```js
+var concatMap = require('concat-map')
+```
+
+concatMap(xs, fn)
+-----------------
+
+Return an array of concatenated elements by calling `fn(x, i)` for each element
+`x` and each index `i` in the array `xs`.
+
+When `fn(x, i)` returns an array, its result will be concatenated with the
+result array. If `fn(x, i)` returns anything else, that value will be pushed
+onto the end of the result array.
+
+## install
+
+With [npm](http://npmjs.org) do:
+
+```sh
+npm install concat-map
+```
+
+## license
+
+MIT
+
+## notes
+
+This module was written while sitting high above the ground in a tree.
+
+[package-url]: https://npmjs.org/package/concat-map
+[npm-version-svg]: https://versionbadg.es/ljharb/concat-map.svg
+[deps-svg]: https://david-dm.org/ljharb/concat-map.svg
+[deps-url]: https://david-dm.org/ljharb/concat-map
+[dev-deps-svg]: https://david-dm.org/ljharb/concat-map/dev-status.svg
+[dev-deps-url]: https://david-dm.org/ljharb/concat-map#info=devDependencies
+[npm-badge-png]: https://nodei.co/npm/concat-map.png?downloads=true&stars=true
+[license-image]: https://img.shields.io/npm/l/concat-map.svg
+[license-url]: LICENSE
+[downloads-image]: https://img.shields.io/npm/dm/concat-map.svg
+[downloads-url]: https://npm-stat.com/charts.html?package=concat-map
+[codecov-image]: https://codecov.io/gh/ljharb/concat-map/branch/main/graphs/badge.svg
+[codecov-url]: https://app.codecov.io/gh/ljharb/concat-map/
+[actions-image]: https://img.shields.io/endpoint?url=https://github-actions-badge-u3jn4tfpocch.runkit.sh/ljharb/concat-map
+[actions-url]: https://github.com/ljharb/concat-map/actions