Add description to codec interfaces

Author: alcaeus

src/Codec/Codec.php

@@ -3,6 +3,9 @@
 namespace MongoDB\Codec;
 
 /**
+ * The Codec interface allows decoding BSON data to native PHP types and back
+ * to BSON.
+ *
  * @psalm-template BSONType
  * @psalm-template NativeType
  * @template-extends Decoder<BSONType, NativeType>

src/Codec/DocumentCodec.php

@@ -5,6 +5,9 @@
 use MongoDB\BSON\Document;
 
 /**
+ * The DocumentCodec interface allows decoding BSON document data to native PHP
+ * objects and back to BSON documents.
+ *
  * @psalm-template ObjectType of object
  * @template-extends Codec<Document, ObjectType>
  */

src/Codec/KnowsCodecLibrary.php

@@ -2,6 +2,11 @@
 
 namespace MongoDB\Codec;
 
+/**
+ * This interface is used to indicate that a class is aware of the CodecLibrary
+ * it was added to. The library will be injected when the codec is added to the
+ * library. This allows codecs to recursively encode its nested values.
+ */
 interface KnowsCodecLibrary
 {
     public function attachLibrary(CodecLibrary $library): void;