Update 'README.md'

README.md

@@ -2,11 +2,24 @@
 
 This package allows user to connect to a labkey server through a slicer interface.
 
+### Cloning
+
+Since there is no `master` branch, git clone will report 
+
+```bash
+warning: remote HEAD refers to nonexistent ref, unable to checkout.
+```
+
+Which is just a warning. Simply move to SlicerLabkeyExtension directory and checkout the SlicerExtensionIndex branch.
+
+### Use in Slicer
+
 To use, add path to unpackaged labkeySlicerPythonAPI/labkeySlicerPythonExtension to
 Additional module paths in Slicer->Edit->Application Settings->Modules submenu. You'll
 also need the SlicerLabkeyDICOMtools package, also available from wiscgit.
 
 Then the package will appear under LabKey.
+
 ![labkeyBrowser](labkeyBrowser/Resources/Screenshots/slicerLabkeyExtensionCaption.png)
 
 If you are interested in the code, you should look at slicerNetwork.py which