Fixed docs links (#9344)

* [add-offline-support] Fixed docs links

* [add-a-manifest-file] Fixed docs links

* [add-page-metadata] Fixed docs link

docs/docs/add-a-manifest-file.md

@@ -2,11 +2,11 @@
 title: Add a manifest file
 ---
 
-If you've run an [audit with Lighthouse](/audit-with-lighthouse/), you may have noticed a lackluster score in the "Progressive Web App" category. Let's address how you can improve that score.
+If you've run an [audit with Lighthouse](/docs/audit-with-lighthouse/), you may have noticed a lackluster score in the "Progressive Web App" category. Let's address how you can improve that score.
 
 But first, what exactly _are_ PWAs?
 
-They are regular websites that take advantage of modern browser functionality to augment the web experience with app-like features and benefits. Check out [Google's overview](https://developers.google.com/web/progressive-web-apps/) of what defines a PWA experience and the [Progressive web apps (PWAs) doc](/progressive-web-app/) to learn how a Gatsby site is a progressive web app.
+They are regular websites that take advantage of modern browser functionality to augment the web experience with app-like features and benefits. Check out [Google's overview](https://developers.google.com/web/progressive-web-apps/) of what defines a PWA experience and the [Progressive web apps (PWAs) doc](/docs/progressive-web-app/) to learn how a Gatsby site is a progressive web app.
 
 Inclusion of a web app manifest is one of the three generally accepted [baseline requirements for a PWA](https://alistapart.com/article/yes-that-web-project-should-be-a-pwa#section1).
 

docs/docs/add-offline-support.md

@@ -2,9 +2,9 @@
 title: Add offline support
 ---
 
-If you've run an [audit with Lighthouse](/audit-with-lighthouse/), you may have noticed a lackluster score in the "Progressive Web App" category. Let's address how you can improve that score.
+If you've run an [audit with Lighthouse](/docs/audit-with-lighthouse/), you may have noticed a lackluster score in the "Progressive Web App" category. Let's address how you can improve that score.
 
-1.  You can [add a manifest file](/add-a-manifest-file/).
+1.  You can [add a manifest file](/docs/add-a-manifest-file/).
 2.  You can also add offline support, since another requirement for a website to qualify as a PWA is the use of a [service worker](https://developer.mozilla.org/en-US/docs/Web/API/Service_Worker_API). A service worker runs in the background, deciding to serve network or cached content based on connectivity, allowing for a seamless, managed offline experience.
 
 [Gatsby's offline plugin](/packages/gatsby-plugin-offline/) makes a Gatsby site work offline--and makes it more resistant to bad network conditions--by creating a service worker for your site.
@@ -35,4 +35,4 @@ npm install --save gatsby-plugin-offline
 
 That's all you need to get started with service workers with Gatsby.
 
-> 💡 If you are also [adding a manifest file](add-a-manifest-file), the manifest plugin should be listed _before_ the offline plugin so that the offline plugin can cache the created `manifest.webmanifest`.
+> 💡 If you are also [adding a manifest file](/docs/add-a-manifest-file/), the manifest plugin should be listed _before_ the offline plugin so that the offline plugin can cache the created `manifest.webmanifest`.

docs/docs/add-page-metadata.md

@@ -2,7 +2,7 @@
 title: Adding page metadata
 ---
 
-If you've run an [audit with Lighthouse](/audit-with-lighthouse/), you may have noticed a lackluster score in the "SEO" category. Let's address how you can improve that score.
+If you've run an [audit with Lighthouse](/docs/audit-with-lighthouse/), you may have noticed a lackluster score in the "SEO" category. Let's address how you can improve that score.
 
 Adding metadata to pages (such as a title or description) are key in helping search engines like Google understand your content, and decide when to surface it in search results.