Add English plugin documentation and update help links

Author: Kouda-Titanium

src/main/resources/en/plugin/index.md

@@ -0,0 +1,140 @@
+# Plugin
+
+KanbanBro plugins are a mechanism for extending the behavior of pages displayed by KanbanBro.
+
+## Plugin syntax
+
+A plugin consists of the following three parts:
+
+- Magic comment
+- Metadata section
+- Body
+
+### Magic comment
+
+Use the following magic comment to mark the script as a KanbanBro plugin.
+
+```javascript
+// @KanbanBroPlugin
+```
+
+### Metadata section
+
+The metadata section contains the plugin's metadata.
+
+It is JSON code commented out with `// `.
+
+---
+
+Example:
+
+```javascript
+// {
+//     "name": "com.example.example_plugin",
+//     "title": "Example Plugin",
+//     "version": "1.0.0",
+//     "description": "This is <b>an example</b> plugin."
+// }
+```
+
+### Body
+
+The body is JavaScript code that implements the plugin's behavior.
+
+To avoid conflicts with the metadata section, the first line of the body must not be a line comment.
+
+The body is generally free-form, but in many cases it includes a check so it runs only on specific pages.
+
+---
+
+Example:
+
+```javascript
+if (location.href === 'https://example.com/') {
+    console.log('This is example.com');
+}
+```
+
+### Example
+
+Below is a complete plugin example.
+
+```javascript
+// @KanbanBroPlugin
+// {
+//     "name": "com.example.example_plugin",
+//     "title": "Example Plugin",
+//     "version": "1.0.0",
+//     "description": "This is <b>an example</b> plugin."
+// }
+
+if (location.href === 'https://example.com/') {
+    console.log('This is example.com');
+}
+```
+
+## File name
+
+The plugin file must have the `.kbb.js` extension.
+
+More precisely, the URL from which the plugin is downloaded is expected to end with `.kbb.js`.
+
+## Metadata
+
+### `name` : required string
+
+A name that uniquely identifies the plugin.
+
+The name is expected to follow an identifier-like format separated by dots, similar to a Java package name.
+
+Each identifier component is expected to consist of one or more lowercase ASCII letters, digits, or underscores (`/[a-z0-9_]+/`).
+
+Example: `com.example.example_plugin`
+
+### `title` : required string
+
+A human-readable title for the plugin.
+
+The title does not have to be in English.
+
+We recommend up to 10 full-width characters or 20 half-width characters.
+
+Example: `Example Plugin`
+
+### `version` : required string
+
+The plugin version.
+
+The version is expected to be the `version core` of [Semantic Versioning](https://semver.org/) (`/([1-9][0-9]*)\.([1-9][0-9]*)\.([1-9][0-9]*)/`).
+
+Example: `1.0.0`
+
+### `description` : required string
+
+A description of the plugin.
+
+It does not have to be in English.
+
+The description supports a subset of HTML, which is rendered on Android by the following code:
+
+<code>textView.<a href="https://developer.android.com/reference/android/widget/TextView#setText(int)">setText</a>(Html.<a href="https://developer.android.com/reference/android/text/Html#fromHtml(java.lang.String,%20int)">fromHtml</a>(description, Html.FROM_HTML_MODE_COMPACT))</code>
+
+Example: `This is <b>an example</b> plugin.`
+
+## Plugin behavior
+
+Plugins are executed as JavaScript after the page has fully loaded.
+
+Therefore, you do not need to wait for the onload event.
+
+---
+
+You cannot use `await` directly in the plugin body.
+
+If you want to use `await`, wrap the code in a `Promise` as follows:
+
+```javascript
+new Promise(async () => {
+    // Code that uses await
+});
+```

src/main/resources/help.md

@@ -72,7 +72,7 @@
 
 - [Heartbeat Guide](en/heartbeat/index.md)
 - [Promotion Code Usage Guide](en/promotion-code/index.md)
-- [プラグイン (Japanese)](ja/plugin/index.md)
+- [Plugin](en/plugin/index.md)
 
 ### 日本語