Update changelog and add credit

Related to #1951

CONTRIBUTORS.md

@@ -188,6 +188,7 @@ video tutorials.
  - Joao da Silva
  - Daniel Sieger
  - Daniel Skorupski
+ - Slemmie
  - Anthony Smith
  - Bradley Smith
  - Cliff Smolinsky

README.md

@@ -280,6 +280,7 @@ information on what to include when reporting a bug.
  - [X11] Bugfix: `glfwPostEmptyEvent` could be ignored due to race condition
    (#379,#1281,#1285,#2033)
  - [X11] Bugfix: Dynamic loading on NetBSD failed due to soname differences
+ - [X11] Bugfix: Left shift of int constant relied on undefined behavior (#1951)
  - [Wayland] Added dynamic loading of all Wayland libraries
  - [Wayland] Added support for key names via xkbcommon
  - [Wayland] Removed support for `wl_shell` (#1443)