Doc: resource manager (#428)

* doc: resource manager

* Update resource-manager.md

docs/resource-manager.md

@@ -51,7 +51,12 @@ this.engine.resourceManager.cancelNotLoaded("test.gltf");
 
 > Note: Currently, unloading unfinished resources will throw an exception.
 
-### 4. Resource Release
+
+### 4. Get loaded resource
+
+Loaded resources will be cached in *ResourceManager*, to get the loaded assets, you should call the `load` method again.
+
+### 5. Resource Release
 
 In order to avoid reloading resources, when the resources are loaded, they will be cached in _ResourceManager_. The cache itself takes up memory and video memory. When developers no longer need the cached content, they need to manually release the cached content.
 
@@ -127,7 +132,6 @@ engine.resourceManager
 
 HDR Loader use [AssetType.HDR](${api}core/AssetType#HDR) to load texture with .HDR format，The resulting product is also a cube texture.
 
-
 ### 4. Environment
 Oasis supports offline baking through [Oasis Editor](https://oasis.alipay.com/editor) or [glTF Viewer](https://oasisengine.cn/gltf-viewer) to get IBL baked products `*.env` file.
 
@@ -202,4 +206,4 @@ export class FBXLoader extends Loader<FBXResource> {
 1. Use the [@resourceLoader](${api}core/resourceLoader) decorator to mark it as _ResourceLoader_, and pass in the type enumeration and the parsed resource suffix name. The above example `FBX` is a type enumeration, `["fbx"]` is the suffix name of the resource being parsed.
 1. Override the [load](${api}core/ResourceManager#load) method, the `load` method will pass in `loadItem` and `resourceManager`, `loadItem` contains the basic information of loading, `resourceManager` can help Load other reference resources.
 1. Return the [AssetPromise](${api}core/AssetPromise) object, `resolve` the resolved resource result, for example, FBX returns a specific `FBXResource`.
-1. If an error is reported, it will be `reject` error.
+1. If an error is reported, it will be `reject` error.

docs/resource-manager.zh-CN.md

@@ -52,7 +52,9 @@ this.engine.resourceManager.cancelNotLoaded("test.gltf");
 > 注意：目前取消加载未完成资源会抛出异常。
 
 
-### 4. 资源释放
+### 4. 获取加载过的资产
+目前加载过的资产会缓存在 *ResourceManager* 中，如需获取加载过的资产，只需要再次调用 `load` 方法即可。
+### 5. 资源释放
 为了避免重复加载资源，当资源被加载完成之后，会被缓存在 *ResourceManager* 内。缓存本身会占用内存和显存，当开发者不再需要缓存的内容时，需要手动去释放缓存的内容。
 
 > 注意：资源之间是相互依赖的。