Some links of Lean recipes in README are broken due to inconsistent naming

[utensil]

Some links of Lean recipes in README are broken due to inconsistent naming:

See <recipes/plain-lean4.lean>, <recipes/lean4-tactics.rst>, <recipes/lean4-tactics-myst.md>__ and <recipes/literate-lean4.lean>__ for examples.

Only the first link works, the rest are broken because the actual file names used underscores instead of hyphens.

Links in the Lean 3 section are OK as far as I've checked.

P.S. Could it be consistent whether the lean3/4 is the prefix? It's better if they are all prefix, so they are listed together in the directory.

[cpitclaudel]

Thanks a lot for spotting this. Could you / Would you like to prepare a PR?

[utensil]

Yes I can, and I guess they can be renamed to using underscore to keep consistency with other files (like the coq ones) .

P.S. lean4-tactics* are no longer there, so languages are all postfixes.