agnoster: stronger warning about changing SEGMENT_SEPARATOR character

themes/agnoster.zsh-theme

@@ -43,7 +43,8 @@ CURRENT_BG='NONE'
   # This is defined using a Unicode escape sequence so it is unambiguously readable, regardless of
   # what font the user is viewing this source code in. Do not replace the
   # escape sequence with a single literal character.
-  SEGMENT_SEPARATOR=$'\ue0b0' # 
+  # Do not change this! Do not make it '\u2b80'; that is the old, wrong code point.
+  SEGMENT_SEPARATOR=$'\ue0b0'
 }
 
 # Begin a segment