Update README.md

README.md

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 # Web Performance Checklist
 A checklist to make sure you website will be fast!
+
+
+## HTML
+
+* critical link tags are in head
+* less critical link tags are end of body
+* less critical link tags lazy load
+  * `<link rel="preload" as="style" onload="this.rel='stylesheet'" id='dashicons-css' `
+* JS loads with the async property
+  * `<script async src="https://hi.js"></script>`
+
+## Fonts
+
+* Fonts should always load `woff2` first
+* `woff` for fallback
+* You can use `font-display: swap;` to allow the browser to use a fallback font while custom font files are being downloaded.
+* eot, or truetype is only needed for `IE < 10`
+
+
+## CSS
+
+* Avoid expensive selectors when possible
+  * `border-radius`
+  * `box-shadow`
+  * `transform`
+  * `filter`
+  * `:nth-child`
+  * `position: fixed;`
+  * Partial matching: `[class^="wrap"]`
+* Don't use universal selectors
+  * Universal selectors like `*, [disabled], [type=“text”]`, etc. are very expensive for the browser to match, as every element in the DOM must be checked.
+* Avoid deeply nested dependent selectors
+  * The descendant selector is very costly, as the browser must check for a match with every descendant element. On a complex web page, this can result in thousands and thousands (perhaps even more) of descendant selector searches.
+
+## JS
+
+* Bundles should always be minified
+* Bundles should have 0 comments, and all license text extracted to a separate file
+
+## Assets
+
+* All assets should be fingerprinted
+* All assets should have `Cache-Control: max-age=365000000, immutable` as a header
+* Assets should be served over http/2
+* Assets should only be served on a cookieless domain
+* All files should be cached by a CDN
+* Support Brotli compression
+  * 15-30% smaller than gzip
+* Compress with gzip, or zopfli as a fallback to brotli
+*  
+  
+## PWA
+* Use a service worker to cache assets
+* Use a service worker to prefetch pages users will most likely navigate to next
+* Support offline, and spotty networks
+