Better error handling for view recipe component when recipe is null (Chap. 6)

When there is no recipe to show (recipe is null):
- Don’t display the edit button.
- Inform user (via a message).
Also removing unused div id=“recipe-details”.
Update README.md
Update README.md
Merge pull request #60 from chalin/patch-7-better-handle-recipe-not-found

Better error handling for view recipe component when recipe is null (Ch.6)