Update documentation

README.md

@@ -2,7 +2,7 @@
 
 This unofficial extension allows previewing of Beckhoff TwinCAT 3 files within Azure DevOps. The source code is available on [GitHub](https://github.com/dfreiberger/tc-preview-extension).
 
-It currently supports the `.TcPOU`, `.TcDUT`, `.TcGVL` and `.TcIO` file extensions. Only Structured Text (ST) is supported, so any sections of the code that are in another format such as LD, FBD or UML will not be displayed.
+It currently supports the `.TcPOU`, `.TcDUT`, `.TcGVL` and `.TcIO` file extensions. 
 
 To see a preview of a file, open it from `Repos > Files` and select the Preview tab. You can also see previews within pull requests or from the search view.
 
@@ -12,6 +12,14 @@ It is also possible to copy a link to a specific section of code by clicking the
 
 Pull requests are welcome.
 
+## Limitations
+
+Only Structured Text (ST) is supported, so any sections of the code that are in another format such as LD, FBD or UML will not be displayed.
+
+The Copy link feature only works for the default branch, or for branches that have been actively selected by choosing them in the branch dropdown first before copying the link. This appears to be a limitation of Azure DevOps and the same issue is present when copying links to normal source files.
+
+![Image of select branch dropdown](img/branch_selection.png "Select branch dropdown")
+
 ## Development
 
 To develop locally, create an Azure DevOps organization and publish this extension in dev mode to it.