Proposed changes for 01-sql-basic-queries.md

[mpfl]

Writing my first query

• Requires explicit instructions to go to "Execute SQL" in SQLite

Calculated values

• Suggest expand g into grams and kg into kilograms. Likewise for mg into milligrams for the Challenge underneath.
• Suggest explaining why we use 1000.0 instead of 1000 for calculating weight in kilograms

Functions

• Suggest introducing ROUND in a little more detail and how ROUND(weight/1000.0, 2) will take the value of weight/1000.0 and round to two decimal places.

Escaping STRING

• Suggest adding an explanatory box about why we escape STRING but not other data types. Can use both single quotes (') and double quotes (") for escaping.

Filtering

• Suggest adding explanatory box about operators i.e. <, <=, >, >=, =, !=