Add note about rotate/merge

Closes #1805

issues.md

@@ -128,7 +128,11 @@ When exporting, LosslessCut may be unable to process certain proprietary tracks.
 
 ## Multiple LosslessCut instances
 
-By default, only a single running instance of LosslessCut is allowed. If you start a new LosslessCut instance from the command line, it will instead pass the list of files onto the already running instance. You can override this behavior inside settings Note that this is **(experimental)**, because Electron doesn't seem to support this. [More info](https://github.com/electron/electron/issues/2493) [#1641](https://github.com/mifi/lossless-cut/issues/1641) 
+By default, only a single running instance of LosslessCut is allowed. If you start a new LosslessCut instance from the command line, it will instead pass the list of files onto the already running instance. You can override this behavior inside settings Note that this is **(experimental)**, because Electron doesn't seem to support this. [More info](https://github.com/electron/electron/issues/2493) [#1641](https://github.com/mifi/lossless-cut/issues/1641)
+
+## Rotation and merging
+
+A video’s rotation is just metadata stored in its file. A file can only have a single rotation across the whole file, so if you have two video files and you rotate only one file and then concatenate them, there will be only one output rotation.
 
 # Still cannot find an answer?