fix: restore markdown link, github link

Author: bluejoyq

2021 - Archive/concurrent-react/legacy-concurrent-react/apis/hidden.md

@@ -15,7 +15,7 @@ the hidden tabs can be deprioritized.
 
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-> Next: [Roots](/apis/roots.md)
+> Next: [Roots](./roots.md)
 
 ---
 

2021 - Archive/concurrent-react/legacy-concurrent-react/apis/react-cache.md

@@ -85,7 +85,7 @@ Other APIs:
 
 ---
 
-> Next: [hidden](/apis/hidden.md)
+> Next: [hidden](./hidden.md)
 
 ---
 

2021 - Archive/concurrent-react/legacy-concurrent-react/apis/roots.md

@@ -88,7 +88,7 @@ work.commit();
 
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-> Next: [Community Demos](/community/demos.md)
+> Next: [Community Demos](../community/demos.md)
 
 ---
 

2021 - Archive/concurrent-react/legacy-concurrent-react/apis/time-slicing.md

@@ -75,13 +75,13 @@ Also see the Time Slicing Fixture: [Live Demo](https://timeslicing-unstable-demo
 
 ---
 
-> Next: [React Suspense](/apis/react-suspense.md)
+> Next: [React Suspense](./react-suspense.md)
 
 ---
 
 **Recommended Sources for further info:**
 
 - [Scheduling is the Future - aweary's talk on React scheduling and Just Noticeable Difference](https://www.youtube.com/watch?v=Iyrf52cwxQI)
 - [The Evolution of React and GraphQL at Facebook - F8 2017](https://developers.facebook.com/videos/f8-2017/the-evolution-of-react-and-graphql-at-facebook-and-beyond/)
-- JSConf Iceland 2018 - [Video](https://www.youtube.com/watch?v=nLF0n9SACd4) and [Source Code](https://github.com/facebook/react/tree/master/fixtures/unstable-async/time-slicing)
+- JSConf Iceland 2018 - [Video](https://www.youtube.com/watch?v=nLF0n9SACd4) and [Source Code](https://github.com/facebook/react/tree/16.8.6/fixtures/unstable-async/time-slicing)
 - [Time Slicing Umbrella Issue](https://github.com/facebook/react/issues/13306)