Expand glossary

[wamirez]

When updating the front page, there's possibly a chain of terms that might get added to it that won't allow for understanding if no definition is given.

Add definitions (links to Wikipedia, maybe?) to the following terms:

• Composable data
• Types
• Functions
• Files
• Unix process
• Nix values
• Nix expressions
• Language
• Building/deploying/distributing software