Update README and dev guide with Java 8 config for Kotlin.

Setting the target conpatibility only seems to work for Java. Added the
equivalent Kotlin config options to the docs.

Issue:#5276
PiperOrigin-RevId: 228482496

README.md

@@ -27,6 +27,8 @@ repository and depend on the modules locally.
 
 
 ### From JCenter ###
 ### From JCenter ###
 
 
+#### 1. Add repositories ####
+
 The easiest way to get started using ExoPlayer is to add it as a gradle
 The easiest way to get started using ExoPlayer is to add it as a gradle
 dependency. You need to make sure you have the Google and JCenter repositories
 dependency. You need to make sure you have the Google and JCenter repositories
 included in the `build.gradle` file in the root of your project:
 included in the `build.gradle` file in the root of your project:
@@ -38,6 +40,8 @@ repositories {
 }
 }
 ```
 ```
 
 
+#### 2. Add ExoPlayer module dependencies ####
+
 Next add a dependency in the `build.gradle` file of your app module. The
 Next add a dependency in the `build.gradle` file of your app module. The
 following will add a dependency to the full library:
 following will add a dependency to the full library:
 
 
@@ -45,15 +49,7 @@ following will add a dependency to the full library:
 implementation 'com.google.android.exoplayer:exoplayer:2.X.X'
 implementation 'com.google.android.exoplayer:exoplayer:2.X.X'
 ```
 ```
 
 
-where `2.X.X` is your preferred version. If not enabled already, you also need
-to turn on Java 8 support in all `build.gradle` files depending on ExoPlayer, by
-adding the following to the `android` section:
-
-```gradle
-compileOptions {
-    targetCompatibility JavaVersion.VERSION_1_8
-}
-```
+where `2.X.X` is your preferred version.
 
 
 As an alternative to the full library, you can depend on only the library
 As an alternative to the full library, you can depend on only the library
 modules that you actually need. For example the following will add dependencies
 modules that you actually need. For example the following will add dependencies
@@ -87,6 +83,32 @@ JCenter can be found on [Bintray][].
 [extensions directory]: https://github.com/google/ExoPlayer/tree/release-v2/extensions/
 [extensions directory]: https://github.com/google/ExoPlayer/tree/release-v2/extensions/
 [Bintray]: https://bintray.com/google/exoplayer
 [Bintray]: https://bintray.com/google/exoplayer
 
 
+#### 3. Turn on Java 8 support ####
+
+If not enabled already, you also need to turn on Java 8 support in all
+`build.gradle` files depending on ExoPlayer, by adding the following to the
+`android` section:
+
+```gradle
+compileOptions {
+  targetCompatibility JavaVersion.VERSION_1_8
+}
+```
+
+Note that if you want to use Java 8 features in your own code, the following
+additional options need to be set:
+
+```gradle
+// For Java compilers:
+compileOptions {
+  sourceCompatibility JavaVersion.VERSION_1_8
+}
+// For Kotlin compilers:
+kotlinOptions {
+  jvmTarget = JavaVersion.VERSION_1_8
+}
+```
+
 ### Locally ###
 ### Locally ###
 
 
 Cloning the repository and depending on the modules locally is required when
 Cloning the repository and depending on the modules locally is required when