Improve videos section in readme (#3285)

* Add a link to talk about the history of structured concurrency in kotlinx.coroutines
* Sightly reorder videos section and remove way too obsolete introduction that is covered by coroutines in practice

Fixes #3273

Author: qwwdfsad

README.md

@@ -61,9 +61,9 @@ suspend fun main() = coroutineScope {
 ## Documentation
 
 * Presentations and videos:
-  * [Introduction to Coroutines](https://www.youtube.com/watch?v=_hfBv0a09Jc) (Roman Elizarov at KotlinConf 2017, [slides](https://www.slideshare.net/elizarov/introduction-to-coroutines-kotlinconf-2017))
-  * [Deep dive into Coroutines](https://www.youtube.com/watch?v=YrrUCSi72E8) (Roman Elizarov at KotlinConf 2017, [slides](https://www.slideshare.net/elizarov/deep-dive-into-coroutines-on-jvm-kotlinconf-2017))
   * [Kotlin Coroutines in Practice](https://www.youtube.com/watch?v=a3agLJQ6vt8) (Roman Elizarov at KotlinConf 2018, [slides](https://www.slideshare.net/elizarov/kotlin-coroutines-in-practice-kotlinconf-2018))
+  * [Deep Dive into Coroutines](https://www.youtube.com/watch?v=YrrUCSi72E8) (Roman Elizarov at KotlinConf 2017, [slides](https://www.slideshare.net/elizarov/deep-dive-into-coroutines-on-jvm-kotlinconf-2017))
+  * [History of Structured Concurrency in Coroutines](https://www.youtube.com/watch?v=Mj5P47F6nJg) (Roman Elizarov at Hydra 2019, [slides](https://speakerdeck.com/elizarov/structured-concurrency))
 * Guides and manuals: 
   * [Guide to kotlinx.coroutines by example](https://kotlinlang.org/docs/coroutines-guide.html) (**read it first**)
   * [Guide to UI programming with coroutines](ui/coroutines-guide-ui.md)