Add adapters concept

Author: octylFractal

source/api/concepts/adapters.rst

@@ -0,0 +1,15 @@
+Adapters
+========
+WorldEdit works across many Minecraft modding platforms. This implies that WorldEdit's API does not use any platform's
+API types, such as Bukkit's ``Player`` or Sponge's ``World``. Instead, WorldEdit has its own set of API types,
+and the platform-specific library (see :ref:`api-libraries`) contains an `adapter` class to turn the platform's
+API types into WorldEdit's API types, and vice versa. For example, you can turn an
+``org.bukkit.entity.Player`` into a ``com.sk89q.worldedit.entity.Player`` like so
+
+.. code-block:: java
+
+    org.bukkit.entity.Player player = /* get a player */;
+    Player wePlayer = BukkitAdapter.adapt(player);
+
+Nearly every other WorldEdit type has a similar conversion from the platform type. These are best discovered by
+looking at the methods in the adapter classes in your IDE.

source/api/concepts/index.rst

@@ -14,3 +14,4 @@ be read in the order provided, as later concepts sometimes reference earlier con
     regions
     registries
     edit-sessions
+    adapters

source/api/index.rst

@@ -13,6 +13,11 @@ WorldEdit provides a stable public interface for other mods and plugins to build
 platform-independent interfaces and classes for working with Minecraft blocks, biomes, and worlds.
 Limited entity support is present as well.
 
+.. _api-libraries:
+
+API Libraries
+-------------
+
 You can get the API via a `Maven repository`_, compatible with Maven_, Gradle_, sbt_, and many other build systems.
 The repository is `<https://maven.enginehub.org/>`_, and WorldEdit is under the group ``com.sk89q.worldedit``.
 Depending on which parts of the API you need, choose one of the following names: