explain version and put in extra file

Dependencies

• [2] 6CMTWIKO migrate from pijul 0.12.0 and flakify

Change contents

• file addition: version (-xw-x--x--)
  [1.0]
  + 1.0.0-alpha.38
• replacement in default.nix at line 12
  [2.3847]→[2.3847:3879](∅→∅)
  − version = "1.0.0-alpha.38";
  [2.3847]

  [2.3879]
  + version = lib.fileContents ./version;
• edit in README.md at line 2
  [2.4558]

  [2.4558]
  +

  + prefix aliases for pijul: You only have to type a prefix of a command. If it is ambiguous, *pj* will tell you. If it is not, pijul is called.
• replacement in README.md at line 5
  [2.4559]→[2.4559:4699](∅→∅)
  − prefix aliases for pijul: You only have to type a prefix of a command. If it is ambiguous, pj will tell you. If it is not, pijul is called.
  [2.4559]

  [2.4699]
  + The *pj* version is always the last pijul version for which the command list was updated, plus possibly a suffix.

  + For the current version, lookup the file `version`.
• replacement in README.md at line 10
  [2.4712]→[2.4712:4751](∅→∅)
  − pj is licensed under GPL-2.0 or later.
  [2.4712]
  + *pj* is licensed under GPL-2.0 or later.