Add documentation of SliceView operation.
Add documentation of SliceView operation.

google/neuroglancer,janelia-flyem/neuroglancer,funkey/neuroglancer,google/neuroglancer,seung-lab/neuroglancer,seung-lab/neuroglancer,funkey/neuroglancer,funkey/neuroglancer,google/neuroglancer,google/neuroglancer,google/neuroglancer,google/neuroglancer,google/neuroglancer,google/neuroglancer,seung-lab/neuroglancer,seung-lab/neuroglancer,janelia-flyem/neuroglancer,janelia-flyem/neuroglancer,seung-lab/neuroglancer,janelia-flyem/neuroglancer,funkey/neuroglancer,seung-lab/neuroglancer,janelia-flyem/neuroglancer,seung-lab/neuroglancer