docs: add slidev-addon-tikzjax to addon gallery

[7086cmd]

resolve #1751

[netlify]

✅ Deploy Preview for slidev ready!

Name	Link
🔨 Latest commit	1261ff5
🔍 Latest deploy log	https://app.netlify.com/sites/slidev/deploys/678bb310e3ed01000832ee3d
😎 Deploy Preview	https://deploy-preview-2012--slidev.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[pkg-pr-new]

Open in Stackblitz

@slidev/client

npm i https://pkg.pr.new/slidevjs/slidev/@slidev/client@2012

create-slidev-theme

npm i https://pkg.pr.new/slidevjs/slidev/create-slidev-theme@2012

create-slidev

npm i https://pkg.pr.new/slidevjs/slidev/create-slidev@2012

@slidev/parser

npm i https://pkg.pr.new/slidevjs/slidev/@slidev/parser@2012

@slidev/types

npm i https://pkg.pr.new/slidevjs/slidev/@slidev/types@2012

@slidev/cli

npm i https://pkg.pr.new/slidevjs/slidev/@slidev/cli@2012

commit: 1261ff5