Add header markdown file and inline images to androidx.compose.material3 refdocs

Bug: 197880751
Test: Existing tests
Change-Id: I3b3af895fd2306fc6703fbe77987d624b0e327c9

diff --git a/compose/material3/material3/src/commonMain/kotlin/androidx/compose/material3/NavigationBar.kt b/compose/material3/material3/src/commonMain/kotlin/androidx/compose/material3/NavigationBar.kt
index 8ecc953..d27bb15 100644
--- a/compose/material3/material3/src/commonMain/kotlin/androidx/compose/material3/NavigationBar.kt
+++ b/compose/material3/material3/src/commonMain/kotlin/androidx/compose/material3/NavigationBar.kt

@@ -57,6 +57,8 @@
 import kotlin.math.roundToInt
 
 /**
+ * ![Navigation bar image](https://developer.android.com/images/reference/androidx/compose/material3/navigation-bar.png)
+ *
  * Material Design bottom navigation bar.
  *
  * A bottom navigation bar allows switching between primary destinations in an app.