Fix table formatting in TechnicalIntroduction.rst

Tables currently implemented as grid tables should be converted to list-table, which handles left-justification of text:

- https://openexr.com/en/latest/TechnicalIntroduction.html#levels-and-level-modes
- https://openexr.com/en/latest/TechnicalIntroduction.html#tiled-image

This task requires some basic familiarity with [reStructuredText](https://docutils.sourceforge.io/rst.html) and [sphinx](https://www.sphinx-doc.org/en/master) but the concepts are easy to pick up from other examples. See [Building the Website](https://openexr.com/en/latest/install.html#building-the-website) for how to test the formatting.

Open TechnicalIntroduction.rst and inspect the tables for the “Levels and Level Modes” and “Tiled Image” sections. Follow the Building the Website instructions to test the documentation formatting; done means both tables render with left-justified text.

Written by the indexing model from the issue text.