Start a proper ignore section in the dictionary of sequences

And by "proper ignore section" I simply mean: have the sequences we want to
ignore all gathered together in a really obvious location, and with some
sort of explanation.

src/textual/_ansi_sequences.py

@@ -170,12 +170,6 @@
     # Tmux (Win32 subsystem) sends the following scroll events.
     "\x1b[62~": (Keys.ScrollUp,),
     "\x1b[63~": (Keys.ScrollDown,),
-    # --
-    # Sequences generated by numpad 5. Not sure what it means. (It doesn't
-    # appear in 'infocmp'. Just ignore.
-    "\x1b[E": (Keys.Ignore,),  # Xterm.
-    "\x1b[G": (Keys.Ignore,),  # Linux console.
-    # --
     # Meta/control/escape + pageup/pagedown/insert/delete.
     "\x1b[3;2~": (Keys.ShiftDelete,),  # xterm, gnome-terminal.
     "\x1b[3$": (Keys.ShiftDelete,),  # rxvt
@@ -370,6 +364,15 @@
     "\x1bOx": "8",
     "\x1bOy": "9",
     "\x1bOM": (Keys.Enter,),
+    ############################################################################
+    # The ignore section. Only add sequences here if they are going to be
+    # ignored. Also, when adding a sequence here, please include a note as
+    # to why it is being ignored; ideally citing sources if possible.
+    ############################################################################
+    # The following 2 are inherited from prompt toolkit. They relate to a
+    # press of 5 on the numeric keypad, when *not* in number mode.
+    "\x1b[E": (Keys.Ignore,),  # Xterm.
+    "\x1b[G": (Keys.Ignore,),  # Linux console.
 }
 
 # https://gist.github.com/christianparpart/d8a62cc1ab659194337d73e399004036