Fix image links with baseUrl

Summary:
When using baseUrl in site config, it adds a prefix to all link paths.

But for assets, it doesn't work if you refer to them as `docs/assets/...`, you have to use just `assets/...`. Source: https://github.com/facebook/Docusaurus/issues/861

Reviewed By: passy

Differential Revision: D20796933

fbshipit-source-id: 2346e42b8b548f576a1e143f56ee5236eab55073

docs/tutorial/intro.md

@@ -3,7 +3,7 @@ id: intro
 title: Intro
 ---
 
-![Android App Tutorial](/docs/assets/android-tutorial.png)
+![Android App Tutorial](assets/android-tutorial.png)
 
 In this tutorial, we show you how how easy it is to build a Flipper plugin
 for Android and iOS that extracts data from your native application and

docs/tutorial/js-custom.md

@@ -9,7 +9,7 @@ Displaying your data in a table might work for many use-cases. However, dependin
 ## Replacing the table
 
 For our sea mammals app, we might not only want to see them listed as image URLs in a table but render the actual images in nice little cards. When selecting one of the cards we still want to display all details in the sidebar.
-![Custom cards UI for our sea mammals plugin](/docs/assets/js-custom.png)
+![Custom cards UI for our sea mammals plugin](assets/js-custom.png)
 
 Currently, the default export in our `index.tsx` is from `createTablePlugin`. Now we are going to replace this with a custom React component extending `FlipperPlugin`.
 

docs/tutorial/js-publishing.md

@@ -41,7 +41,7 @@ in the bottom of the left sidebar and selecting the
 "Install Plugins" tab. It may take a few moments for the
 search index to update and your plugin to appear.
 
-![Install plugins](/docs/assets/install-plugins.png)
+![Install plugins](assets/install-plugins.png)
 
 ## Native Distribution
 

docs/tutorial/js-setup.md

@@ -7,7 +7,7 @@ sidebar_label: Building a desktop plugin
 Now that we have the native side covered, let's display the data we're sending
 on the desktop side.
 
-![Custom cards UI for our sea mammals plugin](/docs/assets/js-custom.png)
+![Custom cards UI for our sea mammals plugin](assets/js-custom.png)
 
 ## Dynamic Plugin loading