slight reorg in Readme

Dependencies

• [2] VJ77YABH more efficient undo/redo
• [3] 34TC5SYK record another known issue I don't know how to fix yet
• [4] A2TQYJ6J .
• [5] IDGP4BJZ new known issue with drawings
• [6] 73OCE2MC after much struggle, a brute-force undo
• [*] FS2ITYYH record a known issue
• [*] 242L3OQX bugfix: ensure Cursor_line is always on a text line

Change contents

• replacement in README.md at line 73
  [4.8364]→[2.2372:2477](∅→∅)
  − * Undo/redo can be sluggish in large files. If things get sluggish, killing

  − the process can lose data.
  [4.8364]

  [4.14]
  + * Undo/redo can be sluggish in large files.
• edit in README.md at line 80
  [3.277]

  [9.1190]
  + * If you kill the process, say by force-quitting because things things get

  + sluggish, you can lose data.

  +