Describe 'surrogateescape' in the documentation.

Also, improve some docstring descriptions of the 'errors' parameter.

Closes #14015.
diff --git a/Modules/_io/textio.c b/Modules/_io/textio.c
index cff9c6e..cd751c1 100644
--- a/Modules/_io/textio.c
+++ b/Modules/_io/textio.c
@@ -642,8 +642,9 @@
     "encoding gives the name of the encoding that the stream will be\n"
     "decoded or encoded with. It defaults to locale.getpreferredencoding(False).\n"
     "\n"
-    "errors determines the strictness of encoding and decoding (see the\n"
-    "codecs.register) and defaults to \"strict\".\n"
+    "errors determines the strictness of encoding and decoding (see\n"
+    "help(codecs.Codec) or the documentation for codecs.register) and\n"
+    "defaults to \"strict\".\n"
     "\n"
     "newline controls how line endings are handled. It can be None, '',\n"
     "'\\n', '\\r', and '\\r\\n'.  It works as follows:\n"