docs: add usage section about prettier-plugin-embed

[karlhorky]

Closes #217

Alternative .prettierrc version of the config (downside: untyped):

{
  "plugins": ["prettier-plugin-embed", "prettier-plugin-sql"],
  "embeddedSqlIdentifiers": ["sql"],
  "language": "postgresql",
  "keywordCase": "upper",
}

[changeset-bot]

⚠️ No Changeset found

Latest commit: 4ea4c85

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[karlhorky]

Seems like the CI error is related to the TOML package:

$ pnpm run-s build lint test

> @unts/prettier@0.0.0 build
> run-p build:*


> @unts/prettier@0.0.0 build:r
> r -f cjs


> @unts/prettier@0.0.0 build:ts
> tsc -b

Error [RollupError]: Could not resolve "./languages.js" from "packages/toml/src/index.ts"
    at error (file:///home/runner/work/prettier/prettier/node_modules/.pnpm/rollup@3.26.1/node_modules/rollup/dist/es/shared/node-entry.js:2245:30)
    at ModuleLoader.handleInvalidResolvedId (file:///home/runner/work/prettier/prettier/node_modules/.pnpm/rollup@3.26.1/node_modules/rollup/dist/es/shared/node-entry.js:24632:24)
    at file:///home/runner/work/prettier/prettier/node_modules/.pnpm/rollup@3.26.1/node_modules/rollup/dist/es/shared/node-entry.js:245[9](https://github.com/un-ts/prettier/actions/runs/7152253084/job/19477387552?pr=327#step:6:10)4:26 {
  code: 'UNRESOLVED_IMPORT',
  exporter: './languages.js',
  id: '/home/runner/work/prettier/prettier/packages/toml/src/index.ts',
  watchFiles: [
    '/home/runner/work/prettier/prettier/packages/toml/src/index.ts',
    '/home/runner/work/prettier/prettier/packages/toml/src/options.ts'
  ]
}
ERROR: "build:r" exited with 1.
ERROR: "build" exited with 1.
Error: Process completed with exit code 1.

[JounQin]

No worry, I'll fix the CI issue.

[JounQin]

See privatenumber/tsx#354 (comment)

[JounQin]

@karlhorky Please fix the CI issue about formatting.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (bd624c2) 87.73% compared to head (4ea4c85) 87.73%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #327   +/-   ##
=======================================
  Coverage   87.73%   87.73%           
=======================================
  Files          10       10           
  Lines         163      163           
  Branches       43       43           
=======================================
  Hits          143      143           
  Misses         19       19           
  Partials        1        1           

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