[SjLj] Add ChangeLog for Wasm SjLj support (#16175)

Author: aheejin

ChangeLog.md

@@ -36,6 +36,15 @@ See docs/process.md for more on how version tagging works.
 - The `--bind` flag used to enable embind has been deprecated in favor of
   `-lembind`.  The semantics have not changed and the old flag continues to
   work. (#16087)
+- New setjmp/longjmp support using Wasm EH instructions is added, which is
+  faster and reduces code size. You need a browser that supports Wasm EH spec to
+  use it. The new SjLj support is enabled by `-sSUPPORT_LONGJMP=wasm`. This can
+  be used with Wasm exception support (`-fwasm-exceptions`), but not with
+  Emscripten exception support (`-fexceptions` or
+  `-sDISABLE_EXCEPTION_CATCHING=0`). When using Wasm EH with Wasm SjLj, there is
+  one restriction that you cannot directly call `setjmp` within a `catch`
+  clause. (Calling another function that calls `setjmp` is fine.)
+  (#14976 and #16072)
 
 3.1.2 - 20/01/2022
 ------------------