chore: remove example results, ignore Results folders

[PSamuele]

 ## What
 - Removes the 35 example result files from `inhouse_potential_optimizer/Results/` (2 runs) and `xfoil_viscous_optimizer/Results/` (3 runs). They were generated before the output fixes (#6), so their `.dat` files were on a single line and `optimization_history.svg` was a PNG.
 - `.gitignore`: `Results/` is now ignored. Every run creates its own folder, and without this every run would leave untracked files.
 - README: the project structure and the Output section say that the Results folders are created by the scripts and not versioned.

 Not touched: `_Original_projects/Original_Python_Project/Results_Re...` (archive of the original project; different folder name, not affected by the new ignore rule).

 ## Verified
 Sandbox: after the clean-up, a run of the in-house optimizer recreates `Results/` and `git status` stays clean.

 ## Depends on
 #13  (base branch: `docs/subfolder-readmes`).