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/18-further-reading/README.md

@@ -5,6 +5,8 @@ You may find more about eBPF in these places:
 - A curated list of awesome projects related to eBPF: <https://github.com/zoidbergwill/awesome-ebpf>
 - A website of eBPF projects and tutorials: <https://ebpf.io/>
 
+> The complete source code: <https://github.com/eunomia-bpf/bpf-developer-tutorial/tree/main/src/18-further-reading>
+
 This is also list of eBPF related papers I read in recent years, might be helpful for people who are interested in eBPF related research.
 
 eBPF (extended Berkeley Packet Filter) is an emerging technology that allows safe execution of user-provided programs in the Linux kernel. It has gained widespread adoption in recent years for accelerating network processing, enhancing observability, and enabling programmable packet processing.