Add some comments to external APIs

[handeyeco]

Summary:

Jeremy asked me to add some comments

[github-actions]

Size Change: +142 B (+0.02%)

Total Size: 873 kB

Filename	Size	Change
packages/perseus-core/dist/es/index.js	30 kB	+55 B (+0.18%)
packages/perseus-score/dist/es/index.js	20.7 kB	+87 B (+0.42%)

ℹ️ View Unchanged

Filename	Size
packages/kas/dist/es/index.js	39.7 kB
packages/keypad-context/dist/es/index.js	760 B
packages/kmath/dist/es/index.js	11.1 kB
packages/math-input/dist/es/index.js	78.2 kB
packages/math-input/dist/es/strings.js	1.79 kB
packages/perseus-editor/dist/es/index.js	276 kB
packages/perseus-linter/dist/es/index.js	22.8 kB
packages/perseus/dist/es/index.js	367 kB
packages/perseus/dist/es/strings.js	6.74 kB
packages/pure-markdown/dist/es/index.js	4.14 kB
packages/simple-markdown/dist/es/index.js	13.1 kB

_{compressed-size-action}

[github-actions]

npm Snapshot: Published

Good news!! We've packaged up the latest commit from this PR (0340bef) and published it to npm. You
can install it using the tag PR2272.

Example:

pnpm add @khanacademy/perseus@PR2272

If you are working in Khan Academy's webapp, you can run:

./dev/tools/bump_perseus_version.sh -t PR2272