Update LSAN docs for aarch64 Linux

[keith]

Currently https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer says:

LeakSanitizer is enabled by default in ASan builds of x86_64 Linux, and can be enabled with ASAN_OPTIONS=detect_leaks=1 on x86_64 OS X

Based on https://github.com/llvm/llvm-project/blob/d1b5a4b0c5dda71176cc32a9b27438a883d05e3c/compiler-rt/lib/sanitizer_common/sanitizer_flags.inc#L77

I believe this should read:

LeakSanitizer is enabled by default in ASAN builds on Linux, and can be enabled with ASAN_OPTIONS=detect_leaks=1 on macOS