Document most common signals (GH-19245) (GH-19257)

Document individual signals (only the most common signals):
description, default action, availability.

(cherry picked from commit 400e1dbcad93061f1f7ab4735202daaa5e731507)
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index feb9285..27cebf3 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -2311,7 +2311,7 @@
 #ifdef SIGXFSZ
     PyOS_setsig(SIGXFSZ, SIG_IGN);
 #endif
-    PyOS_InitInterrupts(); /* May imply initsignal() */
+    PyOS_InitInterrupts(); /* May imply init_signals() */
     if (PyErr_Occurred()) {
         return _PyStatus_ERR("can't import signal");
     }