glyph opsz fall.pdf

@dberlow A couple of small change requests for [glyph opsz fall.pdf]()https://github.com/TypeNetwork/Roboto-Flex/blob/master/docs/Sketch%20Docs/glyph%20opsz%20fall.pdf - none urgent :)

- [ ] Add the `glyph opsz fall.sketch` source file to the repo
- [ ] Remove the `Amstelvar` watermark, this interferes with taking slices of the page into slide decks :)
- [ ] Post the narrative text as a `glyph opsz fall.md` file (or `.txt` or `.rtf`) as copy & paste doesn't work very well with the illustration texts :)
- [ ] I'd like the horizontal comparisons with Amstelvar and Flex, roman and italic, to be more directly comparable with the Century Expanded illusration. The `?` from Amstelvar Roman is great, but the `a` shown in a smaller series, placed in the top right, is a more direct comparison.

- [ ] I'd also like these comparisons to be shown 'vertically', either with a single glyph like `a`, or a short word like `handgloves` (or `shoplift` or a similar early-stage type concepting word you prefer), or short mixed case alphabet (`AaBbCc` of length you prefer), or a complete upper+lower case (`ABC..XYZabc..xyz`). The purpose of showing them vertically is to illustrate this point:

- [ ] There's a few typos; `rational subjective reasoning` -> `rational objective reasoning`; `ca[ height` -> `cap height`; `divide it be text` -> `divide it between text`; `appears shorted` -> appears shorter`; `a upsizing` -> `at upsizing`

- [ ] This paragraph seems incomplete:

- [ ] The final illustration, the step by step way to derive `opsz-min` with parametric axes, uses the test word `Architecture`, but this has no glyph(s) with descenders, so when the text says `As long as these don't appears shorter than the descenders,` we can't see that is the case.

- [ ] I think it is worth proving that if they **DO** appears shorter than the descenders, it looks weird, by providing an illustration that goes "too far"

- [ ] `Finally [we might do something else if I forgot something]...`, well, I think placing the final result on the right of the final step makes it harder to compare, placing it directly under (like the previous steps) would be more helpful

- [ ] I suggest to illustrate proof that you didn't forget anything by adding a final 'overlay' image with the opsz-min style and the parametric style as 50/50 opactity with red/green (or your choice) hue; then you can remove the `Finally...` line from the text :)

- [ ] The steps for 'upsizing' need to be written out :)

- [ ] The 'upsizing' steps are on a 2nd col to the right of the 1st 'downsizing' col, but I don't see any meaning behind having them separated like this, and think it will be better to have them all in a single col, to show that it is a fluid continuous space, and to have the same 50/50 comparison at the top end too