db: Add docstrings to FileUpload; NFC

internal/db/fileupload.go

@@ -31,11 +31,23 @@ type FileUploadState int
 
 // FileUpload models an uploaded file.
 type FileUpload struct {
-	State       FileUploadState
-	ID          uuid.UUID
-	FileName    string
+	// State of the FileUpload (present/deleted/etc).
+	State FileUploadState
+
+	// ID identifies this FileUpload.
+	ID uuid.UUID
+
+	// FileName contains the original filename of this FileUpload.
+	FileName string
+
+	// Content type as determined by http.DetectContentType.
 	ContentType string
-	Checksum    uint32
+
+	// Checksum holds a crc32c checksum of the file.
+	//
+	// This checksum is only meant to allow for the detection of random
+	// database corruption.
+	Checksum uint32
 }
 
 const (