Add serialization as git submodule

Author: daniCsorbaJB

.gitmodules

@@ -0,0 +1,4 @@
+[submodule "kotlinx.serialization"]
+    path = kotlinx-serialization
+    url = https://github.com/Kotlin/kotlinx.serialization
+    branch = doc-restructuring

README.md

@@ -26,16 +26,17 @@ Note that source files for the [server-side landing page](https://kotlinlang.org
 
 #### Sources in different repositories
 
-Source files for the language specification and the docs for coroutines, lincheck, Dokka, and Library creators' guidelines
+Source files for the language specification and the docs for coroutines, serialization, lincheck, Dokka, and Library creators' guidelines
 are stored in separate repositories
 
-| Website page                                                                                     | GitHub repository                                                   |
-|--------------------------------------------------------------------------------------------------|---------------------------------------------------------------------|
-| [Coroutines docs](https://kotlinlang.org/docs/coroutines-guide.html)                             | [kotlinx.coroutines](https://github.com/Kotlin/kotlinx.coroutines/) |
-| [Lincheck docs](https://kotlinlang.org/docs/lincheck-guide.html)                                 | [kotlinx.lincheck](https://github.com/Kotlin/kotlinx-lincheck/)     |
-| [Dokka docs](https://kotlinlang.org/docs/dokka-introduction.html)                                | [Dokka](https://github.com/Kotlin/dokka/)                           |
-| [Library creators' guidelines](https://kotlinlang.org/docs/jvm-api-guidelines-introduction.html) | [api-guidelines](https://github.com/Kotlin/api-guidelines)          |
-| [Language specification](https://kotlinlang.org/spec/introduction.html)                          | [kotlin-spec](https://github.com/Kotlin/kotlin-spec)                |
+| Website page                                                                                     | GitHub repository                                                         |
+|--------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------|
+| [Coroutines docs](https://kotlinlang.org/docs/coroutines-guide.html)                             | [kotlinx.coroutines](https://github.com/Kotlin/kotlinx.coroutines/)       |
+| [Lincheck docs](https://kotlinlang.org/docs/lincheck-guide.html)                                 | [kotlinx.lincheck](https://github.com/Kotlin/kotlinx-lincheck/)           |
+| [Dokka docs](https://kotlinlang.org/docs/dokka-introduction.html)                                | [Dokka](https://github.com/Kotlin/dokka/)                                 |
+| [Serialization docs](https://kotlinlang.org/docs/serialization.html)                             | [kotlinx.serialization](https://github.com/Kotlin/kotlinx.serialization)  | 
+| [Library creators' guidelines](https://kotlinlang.org/docs/jvm-api-guidelines-introduction.html) | [api-guidelines](https://github.com/Kotlin/api-guidelines)                |
+| [Language specification](https://kotlinlang.org/spec/introduction.html)                          | [kotlin-spec](https://github.com/Kotlin/kotlin-spec)                      |
 
 #### Auto-generated content
 

docs/kr.tree

@@ -300,7 +300,9 @@
 		<toc-element toc-title="Coroutines (kotlinx.coroutines)">
 			<include from="kc.tree" origin="coroutines" element-id="coroutines"/>
 		</toc-element>
-		<toc-element toc-title="Serialization (kotlinx.serialization)" topic="serialization.md"/>
+		<toc-element toc-title="Serialization (kotlinx.serialization)">
+			<include from="serialization.tree" origin="serialization" element-id="serialization"/>
+		</toc-element>
 		<toc-element toc-title="Lincheck (kotlinx.lincheck)">
 			<include from="kl.tree" origin="lincheck" element-id="lincheck"/>
 		</toc-element>