fix(fonts): viv-384 iss-621 prefetch preload are not to be used in if…

…rame due to Safa… (#622)

* issue #621: prefetch preload are not to be used in iframe due to Safari issue

* adding remarks

Co-authored-by: yinon <yinon@hotmail.com>

Co-authored-by: yinon <yinon@hotmail.com>

.storybook/preview-head.html

@@ -1,7 +1,3 @@
-<link rel="preload" href="//fonts.resources.vonage.com/fonts/v1/Spezia_Web_Complete_Upright.woff2" as="font"
-	type="font/woff2" crossorigin>
-<link rel="prefetch" href="//fonts.resources.vonage.com/fonts/v1/Spezia_Web_Monospace_Complete.woff2" as="font"
-	type="font/woff2" crossorigin>
 <style>
 	body {
 		outline: none;

common/fonts/readme.md

@@ -47,4 +47,6 @@ Additionally, we suggest to 'decorate' your main HTML with the following optimiz
 Explanation:
 * The first link, `preload`, says to browser that it MUST load our basic, used everywhere font immediatelly.
 While this will still be performed asyncronously, it'll prioritize our main font resource high.
-* The second link, `prefetch`, says to browser that it MAY load our secondary, monospace font sooner than later.
+* The second link, `prefetch`, hints the browser to load our secondary, _monospace_ font, sooner than later.
+
+> Attention! We've found, that `preload` and `prefetch` are **not supported** in Safari (up and include 14) if used in **`iframe`**. Although `iframe` usage is quite rare nowadays, if there is any chance that some HTML will find itself loaded via `iframe`, please do not use the above hints as of now.