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/Makefile

@@ -0,0 +1,23 @@
+# Master Makefile for eBPF tutorials
+# Detects subdirectories with Makefiles and builds them
+
+# Find all subdirectories containing a Makefile
+SUBDIRS := $(shell find . -mindepth 2 -maxdepth 2 -name Makefile -exec dirname {} \; | sort)
+
+# Default target
+all: $(SUBDIRS)
+
+# Build each subdirectory
+$(SUBDIRS):
+	@echo "Building $@"
+	@$(MAKE) -C $@
+
+# Clean all subdirectories
+clean:
+	@for dir in $(SUBDIRS); do \
+		echo "Cleaning $$dir"; \
+		$(MAKE) -C $$dir clean; \
+	done
+
+# Phony targets
+.PHONY: all clean $(SUBDIRS)