org-entities.el (org-entities): Add the "neg" entity

* org-entities.el (org-entities): Add the "neg" entity.

Thanks to Florian beck for triggering this issue.

lisp/org-entities.el

@@ -318,6 +318,7 @@ loaded, add these packages to `org-export-latex-packages-alist'."
     ("prop" "\\propto" t "∝" "[proportional to]" "[proportional to]" "∝")
     ("proptp" "\\propto" t "∝" "[proportional to]" "[proportional to]" "∝")
     ("not" "\\textlnot{}" nil "¬" "[angled dash]" "¬" "¬")
+    ("neg" "\\neg{}" nil "¬" "[angled dash]" "¬" "¬")
     ("land" "\\land" t "∧" "[logical and]" "[logical and]" "∧")
     ("wedge" "\\wedge" t "∧" "[logical and]" "[logical and]" "∧")
     ("lor" "\\lor" t "∨" "[logical or]" "[logical or]" "∨")