Update README.md

Signed-off-by: Matt <mramotar@dropbox.com>

Author: aclassen

README.md

@@ -29,10 +29,14 @@
 
 ### Including Store In Your Project
 
-#### Android
+> **Note**  
+>  
+> **[AtomicFU](https://github.com/Kotlin/kotlinx-atomicfu) is required ([#503](https://github.com/MobileNativeFoundation/Store/issues/503))**
 
+#### Android
 ```kotlin
 implementation "org.mobilenativefoundation.store:store5:5.0.0-alpha03"
+api "org.jetbrains.kotlinx:atomicfu:0.18.5"
 ```
 
 #### Multiplatform (Common, JVM, Native, JS)
@@ -41,6 +45,7 @@ implementation "org.mobilenativefoundation.store:store5:5.0.0-alpha03"
 commonMain {
   dependencies {
     implementation("org.mobilenativefoundation.store:store5:5.0.0-alpha03")
+    api("org.jetbrains.kotlinx:atomicfu:0.18.5")
   }
 }
 ```