add stack overflow plugin to marketplace

Signed-off-by: Emma Indal <emma.indahl@gmail.com>

microsite/data/plugins/stack-overflow.yaml

@@ -0,0 +1,9 @@
+---
+title: Stack Overflow
+author: Spotify
+authorUrl: https://github.com/spotify
+category: Discovery
+description: Provides Stack Overflow specific functionality that can be used in different ways (e.g. for homepage and search) to compose your Backstage App.
+documentation: https://github.com/backstage/backstage/blob/master/plugins/stack-overflow
+iconUrl: img/stack-overflow-logo.svg
+npmPackageName: '@backstage/plugin-adr'

microsite/static/img/stack-overflow-logo.svg

@@ -0,0 +1 @@
+<svg width="100" height="118" fill="none" xmlns="http://www.w3.org/2000/svg"><path d="M84.021 75.825v31H11v-31H0v42h95v-42H84.021z" fill="#BCBBBB"/><path d="M21.057 96.825H74v-10H21.057v10zm1.058-23.915l51.428 10.794 2.117-10.265L24.23 62.645 22.115 72.91zm6.773-24.656l47.618 22.222 4.445-9.524L33.33 38.73l-4.444 9.524zm13.227-23.386l40.423 33.65 6.773-8.042-40.53-33.65-6.666 8.042zM68.147 0L59.68 6.243l31.323 42.222 8.465-6.243L68.147 0z" fill="#F48024"/></svg>

plugins/stack-overflow/README.md

@@ -23,6 +23,8 @@ This stack overflow frontend plugin is primarily responsible for the following:
 
 #### Use specific search result list item for Stack Overflow Question
 
+> Note: For Stack Overflow specific search results to be returned, it needs to be indexed. Use the [stack-overflow-backend plugin](https://github.com/backstage/backstage/blob/master/plugins/stack-overflow-backend/README.md) to index Stack Overflow Questions to search.
+
 When you have your `packages/app/src/components/search/SearchPage.tsx` file ready to make modifications, add the following code snippet to add the `StackOverflowSearchResultListItem` when the type of the search results are `stack-overflow`.
 
 ```tsx