Add cross-platform usage examples and documentation

Co-authored-by: enghitalo <63821277+enghitalo@users.noreply.github.com>

Author: Copilot

vlib/os/notify/EXAMPLES.md

@@ -0,0 +1,98 @@
+# Cross-Platform Usage Example for os.notify
+
+This example demonstrates how to write cross-platform code using `os.notify` that gracefully handles platform differences.
+
+```v
+import os
+import os.notify
+import time
+
+fn main() {
+    mut notifier := notify.new() or {
+        eprintln('Failed to create notifier: ${err}')
+        return
+    }
+    defer {
+        notifier.close() or {}
+    }
+
+    // Create a pipe for demonstration
+    pipefd := [2]int{}
+    if C.pipe(&pipefd[0]) != 0 {
+        eprintln('Failed to create pipe')
+        return
+    }
+    reader, writer := pipefd[0], pipefd[1]
+    defer {
+        os.fd_close(reader)
+        os.fd_close(writer)
+    }
+
+    // Add read event - works on all platforms
+    notifier.add(reader, .read) or {
+        eprintln('Failed to add reader: ${err}')
+        return
+    }
+
+    // Try to add peer_hangup - will fail on macOS, succeed on Linux
+    notifier.add(reader, .peer_hangup) or {
+        // Gracefully handle unsupported feature
+        eprintln('Note: peer_hangup not supported: ${err}')
+        // Continue with just read events
+    }
+
+    // Your event loop
+    for {
+        events := notifier.wait(1 * time.second)
+        for event in events {
+            if event.kind.has(.read) {
+                // Handle read
+                data, _ := os.fd_read(event.fd, 1024)
+                println('Read: ${data}')
+            }
+            if event.kind.has(.peer_hangup) {
+                // This will only trigger on Linux
+                println('Peer disconnected')
+                break
+            }
+        }
+    }
+}
+```
+
+## Platform-Specific Code
+
+You can also use conditional compilation for platform-specific features:
+
+```v
+import os.notify
+
+fn setup_notifier(mut notifier notify.FdNotifier, fd int) ! {
+    $if linux {
+        // Use all available features on Linux
+        notifier.add(fd, .read | .peer_hangup, .edge_trigger)!
+    } $else $if macos {
+        // Use only supported features on macOS
+        notifier.add(fd, .read, .edge_trigger)!
+    }
+}
+```
+
+## Checking Platform Capabilities
+
+For library code that needs to work across platforms, use error handling:
+
+```v
+fn add_with_hangup(mut notifier notify.FdNotifier, fd int) ! {
+    // Try with hangup first
+    notifier.add(fd, .read | .hangup) or {
+        // If it fails, fall back to just read
+        if err.msg().contains('hangup') {
+            notifier.add(fd, .read)!
+        } else {
+            // Some other error, propagate it
+            return err
+        }
+    }
+}
+```