add docs for InputFile

tgbotapi.core/src/commonMain/kotlin/dev/inmo/tgbotapi/requests/abstracts/InputFile.kt

@@ -10,6 +10,17 @@ import kotlinx.serialization.descriptors.*
 import kotlinx.serialization.encoding.Decoder
 import kotlinx.serialization.encoding.Encoder
 
+/**
+ * Common type for all files in Telegram Bot API which can be sent via requests like [dev.inmo.tgbotapi.requests.send.media.SendDocument].
+ * You may use methods like [MPPFile.asMultipartFile] when you want to send files from your file system, but you should
+ * remember about [restrictions][https://core.telegram.org/bots/api#sending-files] in Telegram for bots. In case you
+ * wish to send file by its url, use [FileId] and pass your url as [FileId.fileId]
+ *
+ * @see MPPFile.asMultipartFile
+ * @see ByteArray.asMultipartFile
+ * @see ByteReadChannel.asMultipartFile
+ * @see ByteReadChannelAllocator.asMultipartFile
+ */
 @Serializable(InputFileSerializer::class)
 sealed class InputFile {
     abstract val fileId: String