Add HID-BPF tutorial and implementation for virtual mouse input modification

- Introduced a comprehensive tutorial in README.md explaining how to fix broken HID devices using eBPF without kernel patches.
- Implemented a userspace program (hid-input-modifier.c) that creates a virtual HID mouse using the uhid interface and sends synthetic mouse events.
- Developed a BPF program (hid-input-modifier.bpf.c) that intercepts HID events and modifies mouse movement data, effectively doubling the X and Y movement.
- Created necessary header files (hid_bpf.h, hid_bpf_defs.h, hid_bpf_helpers.h) to define structures and helper functions for the BPF program.
- Added functionality to find and manage the virtual HID device, ensuring seamless integration with the BPF program.

src/features/bpf_wq/README.md

@@ -4,6 +4,8 @@ Ever needed your eBPF program to sleep, allocate memory, or wait for device I/O?
 
 This is what **BPF Workqueues** enable. Created by Benjamin Tissoires at Red Hat in 2024 for HID-BPF device handling, workqueues let you schedule asynchronous work that runs in process context where sleeping and blocking operations are allowed. In this tutorial, we'll explore why workqueues were created, how they differ from timers, and build a complete example demonstrating async callback execution.
 
+> The complete source code: <https://github.com/eunomia-bpf/bpf-developer-tutorial/tree/main/src/features/bpf_wq>
+
 ## Introduction to BPF Workqueues: Solving the Sleep Problem
 
 ### The Problem: When eBPF Can't Sleep