Add missing documentation based on KotlinModule constructor KDoc.

Author: TWiStErRob

src/main/kotlin/com/fasterxml/jackson/module/kotlin/KotlinFeature.kt

@@ -3,11 +3,45 @@ package com.fasterxml.jackson.module.kotlin
 import java.util.BitSet
 import kotlin.math.pow
 
+/**
+ * @see KotlinModule.Builder
+ */
 enum class KotlinFeature(val enabledByDefault: Boolean) {
+    /**
+     * This feature represents whether to deserialize `null` values for collection properties as empty collections.
+     */
     NullToEmptyCollection(enabledByDefault = false),
+
+    /**
+     * This feature represents whether to deserialize `null` values for a map property to an empty map object.
+     */
     NullToEmptyMap(enabledByDefault = false),
+
+    /**
+     * This feature represents whether to treat `null` values as absent when deserializing,
+     * thereby using the default value provided in Kotlin.
+     */
     NullIsSameAsDefault(enabledByDefault = false),
+
+    /**
+     * By default, there's no special handling of singletons (pre-2.10 behavior).
+     * Each time a Singleton object is deserialized a new instance is created.
+     *
+     * When this feature is enabled, it will deserialize then canonicalize (was the default in 2.10).
+     * Deserializing a singleton overwrites the value of the single instance.
+     *
+     * See [jackson-module-kotlin#225]: keep Kotlin singletons as singletons.
+     * @see com.fasterxml.jackson.module.kotlin.SingletonSupport
+     */
     SingletonSupport(enabledByDefault = false),
+
+    /**
+     * This feature represents whether to check deserialized collections.
+     *
+     * With this disabled, the default, collections which are typed to disallow null members (e.g. `List<String>`)
+     * may contain null values after deserialization.
+     * Enabling it protects against this but has significant performance impact.
+     */
     StrictNullChecks(enabledByDefault = false);
 
     internal val bitSet: BitSet = 2.0.pow(ordinal).toInt().toBitSet()