docs: fix icons installation guide (#175)

Author: kermanx

guide/syntax.md

@@ -328,15 +328,15 @@ This is another note
 
 ## Icons
 
-Slidev allows you to have the accessing to almost all the popular open-source iconsets **directly** in your markdown. Powered by [`unplugin-icons`](https://github.com/antfu/unplugin-icons) and [Iconify](https://iconify.design/).
+Slidev allows you to have the accessing to almost all the popular open-source iconsets **directly** in your markdown after installing the corresponding package. Powered by [`unplugin-icons`](https://github.com/antfu/unplugin-icons) and [Iconify](https://iconify.design/).
 
 The naming follows [Iconify](https://iconify.design/)'s conversion `{collection-name}-{icon-name}`. For example:
 
-- `<mdi-account-circle />` - <mdi-account-circle /> from [Material Design Icons](https://github.com/Templarian/MaterialDesign)
-- `<carbon-badge />` - <carbon-badge /> from [Carbon](https://github.com/carbon-design-system/carbon/tree/main/packages/icons)
-- `<uim-rocket />` - <uim-rocket /> from [Unicons Monochrome](https://github.com/Iconscout/unicons)
-- `<twemoji-cat-with-tears-of-joy />` - <twemoji-cat-with-tears-of-joy /> from [Twemoji](https://github.com/twitter/twemoji)
-- `<logos-vue />` - <logos-vue /> from [SVG Logos](https://github.com/gilbarbara/logos)
+- `<mdi-account-circle />` - <mdi-account-circle /> from [Material Design Icons](https://github.com/Templarian/MaterialDesign) - [`@iconify-json/mdi`](https://npmjs.com/package/@iconify-json/mdi)
+- `<carbon-badge />` - <carbon-badge /> from [Carbon](https://github.com/carbon-design-system/carbon/tree/main/packages/icons) - [`@iconify-json/carbon`](https://npmjs.com/package/@iconify-json/carbon)
+- `<uim-rocket />` - <uim-rocket /> from [Unicons Monochrome](https://github.com/Iconscout/unicons) - [`@iconify-json/uim`](https://npmjs.com/package/@iconify-json/uim)
+- `<twemoji-cat-with-tears-of-joy />` - <twemoji-cat-with-tears-of-joy /> from [Twemoji](https://github.com/twitter/twemoji) - [`@iconify-json/twemoji`](https://npmjs.com/package/@iconify-json/twemoji)
+- `<logos-vue />` - <logos-vue /> from [SVG Logos](https://github.com/gilbarbara/logos) - [`@iconify-json/logos`](https://npmjs.com/package/@iconify-json/logos)
 - And much more...
 
 Browse and search for all the icons available with [Icônes](https://icones.js.org/).