Adding dietary tags

[alexandrapurcarea]

This is more of a proposal than an issue, but we should add a few tags once this project gets more traction:

• Meal types: main, dessert, etc.
• Dietary preferences: vegan, vegetarian
• Allergies: gluten, soy etc.
• Other: alcohol

[neanias]

I think this would also be good if we migrate this to a static website in the future too. Something like adding tags and an index. Related, having a cooking glossary might be a good idea!