design: add proposal for a soft memory limit

For golang/go#48409.

Change-Id: I4e5d6d117982f51108dca83a8e59b118c2b6f4bf
Reviewed-on: https://go-review.googlesource.com/c/proposal/+/350116
Reviewed-by: Michael Pratt <[email protected]>

Author: mknyszek

design/48409-soft-memory-limit.md

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+# Design document
+
+The GC pacer design document is generated from the `.src.md` file in this
+directory.
+It contains LaTeX formulas which Markdown cannot render, so they're
+rendered by an external open-source tool,
+[md-latex](https://github.com/mknyszek/md-tools).
+
+Then, because Gitiles' markdown viewer can't render SVGs, run
+
+```
+./svg2png.bash
+cd pacer-plots
+./svg2png.bash
+cd ..
+```
+
+And go back and replace all instances of SVG with PNG in the final document.
+
+Note that `svg2png.bash` requires both ImageMagick and Google Chrome.
+

design/48409/README.md

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+#!/bin/bash
+
+for input in *.svg; do
+	output=${input%.*}.png
+	google-chrome --headless --window-size=1920,1080 --disable-gpu --screenshot $input
+	convert screenshot.png -trim $output
+done
+rm screenshot.png