DOC: X5 warning, missing rst stub

doc/fsl.scripts.fsl_apply_x5.rst

+``fsl.scripts.fsl_apply_x5``
+============================
+
+.. automodule:: fsl.scripts.fsl_apply_x5
+    :members:
+    :undoc-members:
+    :show-inheritance:

doc/fsl.scripts.rst

@@ -5,6 +5,7 @@
    :hidden:
 
    fsl.scripts.atlasq
+   fsl.scripts.fsl_apply_x5
    fsl.scripts.fsl_convert_x5
    fsl.scripts.fsl_ents
    fsl.scripts.imcp

fsl/transform/x5.py

@@ -17,6 +17,9 @@ transformations from/to BIDS X5 files. The following functions are available:
    writeNonLinearX5
 
 
+.. warning:: This is a development release, and is subject to change.
+
+
 An X5 file is a HDF5 container file which stores a linear or non-linear
 transformation from one NIfTI image to another.