docs: add asciidoc docs for use with refinedsites

docs/pages/advanced-usage/using-the-api.adoc

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+= Using the API
+
+== For Minecraft 1.18.2 or later
+
+Starting from Minecraft 1.18, you can include the Refined Storage API in your development environment from 2 sources:
+
+=== GitHub packages
+
+Add the following repository to your `build.gradle`:
+
+[source,groovy]
+----
+repositories {
+    maven {
+        url = uri("https://maven.pkg.github.com/refinedmods/refinedstorage")
+        credentials {
+            username = "anything"
+            password = "\u0067hp_oGjcDFCn8jeTzIj4Ke9pLoEVtpnZMP4VQgaX"
+        }
+    }
+}
+----
+
+The credentials are necessary because as of December 2021, GitHub packages still requires authentication for public packages.
+The password used is a personal access token that has read access to the Refined Mods repositories.
+It can be reused in other projects.
+
+See:
+
+* https://github.community/t/download-from-github-package-registry-without-authentication/14407/38
+* https://github.community/t/download-from-github-package-registry-without-authentication/14407/44
+
+You can find a list of versions on link:https://github.com/orgs/refinedmods/packages[GitHub packages].
+
+=== CreeperHost Maven
+
+Add the following repository to your `build.gradle`:
+
+[source,groovy]
+----
+repositories {
+    maven {
+        url = uri("https://maven.creeperhost.net")
+    }
+}
+----
+
+You can find a list of versions on the link:https://maven.creeperhost.net/com/refinedmods/refinedstorage[Maven index].
+
+**Warning:** Due to a bug in the Maven index on CreeperHost, new versions aren't included in the index.
+However, you can use them in your Gradle dependency.
+
+For example, version `1.10.2` isn't included in the Maven index, but you can use `1.10.2` in your Gradle dependency when using CreeperHost Maven.
+
+== For older Minecraft versions
+
+Some Refined Storage API versions for older Minecraft versions are available on the link:https://maven.creeperhost.net/com/refinedmods/refinedstorage[CreeperHost Maven].
+
+However, not all of them are available.
+If you need a specific version, build Refined Storage yourself and include the API manually.
+
+== Including the API
+
+[source,groovy]
+----
+implementation fg.deobf("com.refinedmods:refinedstorage:VERSION_HERE") {
+    transitive false
+}
+----
+
+== Using the API
+
+Use the `@RSAPIInject` annotation to get access to the API facade.
+
+[source,java]
+----
+public class MyMod {
+    @RSAPIInject
+    public static IRSAPI RSAPI;
+}
+----
+
+== Javadoc
+
+Updated Javadoc is available after every release link:https://refinedmods.com/javadoc/refinedstorage[here].