f readme - note about addr san default

Author: TheBlueMatt

lightning-c-bindings/README.md

@@ -219,4 +219,10 @@ These include:
    ```
    
 **It is highly recommended that you test any code which relies on the C (or C++) bindings in
-valgrind, MemorySanitizer, or other similar tools to ensure correctness.**
+valgrind, AddressSanitizer, MemorySanitizer, or other similar tools to ensure correctness.**
+
+Note that after running `genbindings.sh`, if possible, the static lib in target/debug (eg
+target/debug/liblightning.a) will be linked with address sanitizer. In order to build against it,
+you will need to link with `clang` with `-fsanitize=address` with the same version of LLVM as
+`rustc`'s LLVM. If genbindings.sh failed to find a matching `clang` or you are building on an
+unsupported platform, a warning noting that address sanitizer is not available will be printed.