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/44-scx-simple/README.md

@@ -1,9 +1,11 @@
 # eBPF Tutorial: Introduction to the BPF Scheduler
 
-Welcome to our deep dive into the world of eBPF with a focus on the BPF scheduler! If you're looking to extend your eBPF knowledge beyond the basics, you're in the right place. 
+Welcome to our deep dive into the world of eBPF with a focus on the BPF scheduler! If you're looking to extend your eBPF knowledge beyond the basics, you're in the right place.
 
 In this tutorial, we'll explore the **scx_simple scheduler**, a minimal example of the sched_ext scheduler class introduced in Linux kernel version `6.12`. We'll walk you through its architecture, how it leverages BPF programs to define scheduling behavior, and guide you through compiling and running the example. By the end, you'll have a solid understanding of how to create and manage advanced scheduling policies using eBPF.
 
+> The complete source code: <https://github.com/eunomia-bpf/bpf-developer-tutorial/tree/main/src/44-scx-simple>
+
 ## Understanding the Extensible BPF Scheduler
 
 At the heart of this tutorial is the **sched_ext** scheduler class. Unlike traditional schedulers, sched_ext allows its behavior to be defined dynamically through a set of BPF programs, making it highly flexible and customizable. This means you can implement any scheduling algorithm on top of sched_ext, tailored to your specific needs.