Suggestion: Provide intuition for how data are represented in 2.1

[akshaymehra]

Section 2.1 introduces data definitions, including modality, type, and format.

It would be helpful to provide intuition for how data are represented generally, e.g., continuous vs. discrete values, data organization via databases, the use of lists, matrices, and/or tables, floats vs. integer representation, etc.

These concepts can be linked directly to different existing sections. For example, a reference to matrices/arrays can link to 2.2.

Language-specific definitions, such as DataFrames, then could be moved to sections with code.