Update install_vtk.md

Author: hpjeonGIT

Diff for: install_vtk.md

@@ -1,6 +1,9 @@
 # standard cmake
 - `mkdir build; cd build; ccmake ..`
   - For RHEL7, opengl2.1 might not be able to run regular VTK library
-  - Recompile with `VTK_RENDERING_BACKEND=OpenGL` while the default is OpenGL2
+  - Use 7.1.1
+    - Set `VTK_RENDERING_BACKEND=OpenGL` while the default is OpenGL2
+  - wrap with python or conda when available
+  - Choose python version as 2 or 3
 - `make -j 10; make install`
 - Copy $PREFIX/lib/python3.x/site-packages/vtk to $PYTHONE_HOME/lib/python3.x/site-packages