Add example of mapping from file in system (#3808)

Co-authored-by: Richard North <[email protected]>

Author: kevinrobayna

docs/features/files.md

@@ -1,5 +1,14 @@
 # Files and volumes
 
+## File mapping
+
+It is possible to map a file or directory from your FileSystem into the container as a volume using `withFileSystemBind`:
+```java
+String pathToFile = System.getProperty("user.home") + "/.aws";
+new GenericContainer(...)
+        .withFileSystemBind(pathToFile, "/home/user/.aws", BindMode.READ_ONLY)
+```
+
 ## Volume mapping
 
 It is possible to map a file or directory **on the classpath** into the container as a volume using `withClasspathResourceMapping`: