Document most common signals (GH-19245)

Document individual signals (only the most common signals):
description, default action, availability.
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 4c27738..2d5cb0f 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -2433,7 +2433,7 @@
 #ifdef SIGXFSZ
     PyOS_setsig(SIGXFSZ, SIG_IGN);
 #endif
-    PyOS_InitInterrupts(); /* May imply initsignal() */
+    PyOS_InitInterrupts(); /* May imply init_signals() */
     if (_PyErr_Occurred(tstate)) {
         return _PyStatus_ERR("can't import signal");
     }