docs: add CLAUDE.md for project guidance and create master Makefile for eBPF tutorials

- Introduced CLAUDE.md to provide an overview and guidance for the eBPF Developer Tutorial repository.
- Added a master Makefile to automate the building and cleaning of eBPF tutorial subdirectories.
- Updated .gitignore in the sslsniff example to include the sslsniff binary.
- Made minor code adjustments in user_ringbuf.c and xdp-tcpdump.c to include necessary headers.
- Modified the Makefile in the btf-uprobe example to streamline the build process.

src/35-user-ringbuf/user_ringbuf.c

@@ -4,6 +4,8 @@
 #include <signal.h>
 #include <stdio.h>
 #include <time.h>
+#include <unistd.h>
+#include <string.h>
 #include <sys/resource.h>
 #include <bpf/libbpf.h>
 #include "user_ringbuf.h"