Add explanatory diagram to Rendering overview article

Re:

```
**Exception**: an OBJ with an OAM X position of 0 (thus, completely off the left side of the screen)
always incurs a 11-cycle penalty, regardless of `SCX`.
```

in the new Rendering Overview article

https://github.com/gbdev/pandocs/pull/501#discussion_r1324497903

Open the Rendering Overview article and review the quoted OBJ/OAM X-position exception, then read the linked discussion on PR #501. Done means the article includes an explanatory diagram for that rendering penalty and remains accurate.

Written by the indexing model from the issue text.