[doc] Add documentation for Ray debugger (#11815)

Co-authored-by: Richard Liaw <rliaw@berkeley.edu>

python/ray/scripts/scripts.py

@@ -157,7 +157,7 @@ def dashboard(cluster_config_file, cluster_name, port, remote_port):
     type=str,
     help="Override the address to connect to.")
 def debug(address):
-    """Debug Ray program."""
+    """Show all active breakpoints and exceptions in the Ray debugger."""
     from telnetlib import Telnet
     if not address:
         address = services.find_redis_address_or_die()

python/ray/util/rpdb.py

@@ -170,12 +170,16 @@ def connect_ray_pdb(host=None, port=None, patch_stdstreams=False, quiet=None):
     return rdb
 
 
-def set_trace(host=None, port=None, patch_stdstreams=False, quiet=None):
+def set_trace():
+    """Interrupt the flow of the program and drop into the Ray debugger.
+
+    Can be used within a Ray task or actor.
+    """
     frame = sys._getframe().f_back
-    rdb = connect_ray_pdb(host, port, patch_stdstreams, quiet)
+    rdb = connect_ray_pdb(None, None, False, None)
     rdb.set_trace(frame=frame)
 
 
-def post_mortem(host=None, port=None, patch_stdstreams=False, quiet=None):
-    rdb = connect_ray_pdb(host, port, patch_stdstreams, quiet)
+def post_mortem():
+    rdb = connect_ray_pdb(None, None, False, None)
     rdb.post_mortem()