Merge pull request #319 from jeremy-rifkin/backward-cpp

Add warning about backward::SignalHandling

Closes #319.

README.md

@@ -407,6 +407,12 @@ this object doesn't do anything. It exposes only one method:
 bool loaded() const // true if loaded with success
 ```
 
+**Warning:** The registered signal handlers are not
+[signal safe](https://www.man7.org/linux/man-pages/man7/signal-safety.7.html),
+mostly because backward-cpp and the DWARF decoding libraries are using `malloc`.
+In case a signal is raised while malloc is holding a lock, a deadlock will
+occur.
+
 ### Trace object
 
 To keep the memory footprint of a loaded `StackTrace` on the low-side, there a