Create README for avaje-jex-static-content plugin

Added README.md with installation and usage instructions for the static content plugin.

Author: SentryMan

avaje-jex-static-content/README.md

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+# Static Resources
+
+[![Maven Central](https://img.shields.io/maven-central/v/io.avaje/avaje-jex-static-content.svg?label=Maven%20Central)](https://mvnrepository.com/artifact/io.avaje/avaje-jex-static-content)
+[![javadoc](https://javadoc.io/badge2/io.avaje/avaje-jex-static-content/javadoc.svg?color=purple)](https://javadoc.io/doc/io.avaje/avaje-jex-static-content)
+
+PLugin for serving static resources from the classpath or filesystem.
+
+It provides a `StaticContent` class to configure the location and HTTP path of your static resources, as well as other attributes.
+
+## Installation
+
+Add the static content dependency to your project:
+```xml
+<dependency>
+  <groupId>io.avaje</groupId>
+  <artifactId>avaje-jex-static-content</artifactId>
+  <version>${avaje.jex.version}</version>
+</dependency>
+```
+
+## Basic Usage
+```java
+StaticContent singleFile =
+    StaticContent.ofFile("src/main/resources/example.txt").httpPath("/single").build();
+StaticContent directoryCP =
+    StaticContent.ofClassPath("/public/").httpPath("/").directoryIndex("index.html").build();
+Jex app =
+    Jex.create()
+        .plugin(singleFile) // will serve the src/main/resources/example.txt
+        .plugin(directoryCP); // will serve files from the /public classpath directory
+```
+
+## Configuration Options
+
+| Method | Description |
+|--------|-------------|
+| `directoryIndex("index.html")` | The index file to be served when a directory is requested. |
+| `route("/public")` | Sets the HTTP path and security role for the static resource handler. |
+| `preCompress()` | Sent resources will be pre-compressed and cached in memory when this is enabled. |
+| `putMimeTypeMapping("sus", "application/sus")` | Adds a custom file extension MIME mapping to the configuration. |
+| `putResponseHeader("key", value)` | Adds a new response header to the configuration. |
+| `resourceLoader(clazz)` | Sets a custom resource loader for loading class/module path resources. |
+| `skipFilePredicate(ctx -> !ctx.path().contains("/skip"))` | Sets a predicate to filter files based on the request context. |