Add documentation and update README

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "docs/.shared"]
+	path = docs/.shared
+	url = https://github.com/amphp/website-shared

README.md

@@ -19,22 +19,23 @@ composer require amphp/dns
 
 require __DIR__ . '/vendor/autoload.php';
 
+use Amp\Dns;
 use Amp\Loop;
 
 Loop::run(function () {
-    $githubIpv4 = (yield Amp\Dns\resolve("github.com", $options = ["types" => Amp\Dns\Record::A]));
+    $githubIpv4 = yield Dns\resolve("github.com", Dns\Record::A);
     var_dump($githubIpv4);
 
-    $googleIpv4 = Amp\Dns\resolve("google.com", $options = ["types" => Amp\Dns\Record::A]);
-    $googleIpv6 = Amp\Dns\resolve("google.com", $options = ["types" => Amp\Dns\Record::AAAA]);
+    $googleIpv4 = Amp\Dns\resolve("google.com", Dns\Record::A);
+    $googleIpv6 = Amp\Dns\resolve("google.com", Dns\Record::AAAA);
 
-    $firstGoogleResult = (yield Amp\Promise\first([$googleIpv4, $googleIpv6]));
+    $firstGoogleResult = yield Amp\Promise\first([$googleIpv4, $googleIpv6]);
     var_dump($firstGoogleResult);
 
-    $combinedGoogleResult = (yield Amp\Dns\resolve("google.com"));
+    $combinedGoogleResult = yield Amp\Dns\resolve("google.com");
     var_dump($combinedGoogleResult);
 
-    $googleMx = (yield Amp\Dns\query("google.com", Amp\Dns\Record::MX));
+    $googleMx = yield Amp\Dns\query("google.com", Amp\Dns\Record::MX);
     var_dump($googleMx);
 });
 ```

docs/.gitignore

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+.bundle
+_site
+Gemfile.lock

docs/Gemfile

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+source "https://rubygems.org"
+gem "github-pages"
+gem "kramdown"
+gem "jekyll-github-metadata"
+gem "jekyll-relative-links"

docs/_config.yml

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+kramdown:
+  input: GFM
+  toc_levels: 2..3
+
+baseurl: "/dns"
+layouts_dir: ".shared/layout"
+
+exclude: ["Gemfile", "Gemfile.lock", "README.md", "vendor"]
+include: [".shared"]
+
+repository: amphp/dns
+gems:
+ - "jekyll-github-metadata"
+ - "jekyll-relative-links"
+
+defaults:
+ - scope:
+     path: ""
+     type: "pages"
+   values:
+     layout: "docs"
+
+asset_path: "/dns/.shared/asset"

docs/index.md

@@ -0,0 +1,73 @@
+---
+title: Asynchronous DNS Resolution
+permalink: /
+---
+`amphp/dns` provides asynchronous DNS name resolution for [Amp](http://amphp.org/amp).
+
+## Installation
+
+```bash
+composer require amphp/dns
+```
+
+## Usage
+
+### Configuration
+
+`amphp/dns` automatically detects the system configuration and uses it. On Unix-like systems it reads `/etc/resolv.conf` and respects settings for nameservers, timeouts, and attempts. On Windows it looks up the correct entries in the Windows Registry and takes the listed nameservers. You can pass a custom `ConfigLoader` instance to `BasicResolver` to load another configuration, such as a static config.
+
+It respects the system's hosts file on Unix and Windows based systems, so it works just fine in environments like Docker with named containers.
+
+The package uses a global default resolver with can be accessed and changed via `Amp\Dns\resolver()`. If an argument other than `null` is given, the given resolver is used as global instance. The instance is automatically bound to the current event loop. If you replace the event loop via `Amp\Loop::set()`, then you have to set a new global resolver.
+
+Usually you don't have to change the resolver. If you want to use a custom configuration for a certain request, you just create a new resolver instance and use that instead of changing the global one.
+
+### Address Resolution
+
+`Amp\Dns\resolve` provides hostname to IP address resolution. It returns an array of IPv4 and IPv6 addresses by default. The type of IP addresses returned can be restricted by passing a second argument with the respective time.
+
+```php
+// Example without type restriction. Will return IPv4 and / or IPv6 addresses.
+// What's returned depends on what's available for the given hostname.
+
+/** @var Amp\Dns\Record[] $records */
+$records = yield Amp\Dns\resolve("github.com");
+```
+
+```php
+// Example with type restriction. Will throw an exception if there are no A records.
+
+/** @var Amp\Dns\Record[] $records */
+$records = yield Amp\Dns\resolve("github.com", Amp\Dns\Record::A);
+```
+
+### Custom Queries
+
+`Amp\Dns\query` supports the various other DNS record types such as `MX`, `PTR`, or `TXT`. It automatically rewrites passed IP addresses for `PTR` lookups.
+
+```php
+/** @var Amp\Dns\Record[] $records */
+$records = Amp\Dns\query("google.com", Amp\Dns\Record::MX);
+```
+
+```php
+/** @var Amp\Dns\Record[] $records */
+$records = Amp\Dns\query("8.8.8.8", Amp\Dns\Record::PTR);
+```
+
+### Caching
+
+The `BasicResolver` caches responses by default in an `Amp\Cache\ArrayCache`. You can set any other `Amp\Cache\Cache` implementation by creating a custom instance of `BasicResolver` and setting that via `Amp\Dns\resolver()`, but it's usually unnecessary. If you have a lot of very short running scripts, you might want to consider using a local DNS resolver with a cache instead of setting a custom cache implementation, such as `dnsmasq`. 
+
+### Reloading Configuration
+
+The `BasicResolver` (which is the default resolver shipping with that package) will cache the configuration of `/etc/resolv.conf` / the Windows Registry and the read host files by default. If you wish to reload them, you can set a periodic timer that requests a background reload of the configuration.
+
+```php
+Loop::repeat(60000, function () use ($resolver) {
+    yield Amp\Dns\resolver()->reloadConfig();
+});
+```
+
+{:.note}
+> The above code relies on the resolver not being changed. `reloadConfig` is specific to `BasicResolver` and is not part of the `Resolver` interface. You might want to guard the reloading with an `instanceof` check or manually set a `BasicResolver` instance on startup to be sure it's an instance of `BasicResolver`.