add some comments

Former-commit-id: 0fc6441c9608f0650003a7ab29dd704166345272

src/Makefile

@@ -316,6 +316,7 @@ else
     endef
 endif
 
+# Alpine OS doesn't have support for the execinfo backtrace library we use for debug, so we provide an alternate implementation using libwunwind.
 OS := $(shell cat /etc/os-release | grep ID= | head -n 1 | cut -d'=' -f2)
 ifeq ($(OS),alpine)
     FINAL_CXXFLAGS+=-DUNW_LOCAL_ONLY

src/debug.cpp

@@ -51,6 +51,7 @@ typedef ucontext_t sigcontext_t;
 #include <cxxabi.h>
 #endif /* HAVE_BACKTRACE */
 
+//UNW_LOCAL_ONLY being set means we use libunwind for backtraces instead of execinfo
 #ifdef UNW_LOCAL_ONLY
 #include <libunwind.h>
 #include <cxxabi.h>