Add support for Web App Manifest in siteConfig

[tirthbodawala]

Motivation

To improve user experience and low load time for re-visiting users, I would like to include a service worker to make it a Progressive Web App. Adding service worker is easy with scripts in siteConfig but one would require manifest.json to be able to add it to the home screen. With the current code base, there is no extra field to add manifest.json to the head.

Thus have added an optional field manifest in siteConfig and update the lib/core/Head.js along with docs/api-site-config.md accordingly.

Test Plan

Well as the code implies if the config key exists then create the <link /> tag accordingly. No special test cases are required.

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[endiliey]

Code-wise approved.

Just need extra opinion from @yangshun @JoelMarcey

[yangshun]

Looks great! Thanks for adding this!

[tirthbodawala]

I am glad I was able to contribute! Though it was just a small addition :)

[yangshun]

No contribution is too small. Thanks Tirth!

…

On Mon, Sep 3, 2018, 12:33 AM Tirth Bodawala ***@***.***> wrote: I am glad I was able to contribute! Though it was just a small addition :) — You are receiving this because you modified the open/close state. Reply to this email directly, view it on GitHub <#934 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABQRHQaL5ofNVoTpcbddB9YZt9VyRx7Kks5uXNtjgaJpZM4WUtx0> .