Move "Citing" section into its own document

Author: jcfr

citing.md

@@ -0,0 +1,17 @@
+# Citing
+
+When citing VTK in your scientific research, please mention the following work to support increased visibility and dissemination of our software:
+
+> Schroeder, Will; Martin, Ken; Lorensen, Bill (2006), The Visualization Toolkit (4th ed.), Kitware, ISBN 978-1-930934-19-1
+
+For your convenience here is a bibtex entry:
+
+```bibtex
+@Book{vtkBook,
+  author    = "Will Schroeder and Ken Martin and Bill Lorensen",
+  title     = "The Visualization Toolkit (4th ed.)",
+  publisher = "Kitware",
+  year      = "2006",
+  isbn      = "978-1-930934-19-1",
+}
+```

index.md

@@ -9,22 +9,6 @@ resources for the fourth edition of the  [VTK textbook](https://vtk.org/vtk-text
 :caption: Contents
 :glob:
 about_page
+citing
 VTKBook/*
 ```
-## Citing
-
-When citing VTK in your scientific research, please mention the following work to support increased visibility and dissemination of our software:
-
-> Schroeder, Will; Martin, Ken; Lorensen, Bill (2006), The Visualization Toolkit (4th ed.), Kitware, ISBN 978-1-930934-19-1
-
-For your convenience here is a bibtex entry:
-
-```bibtex
-@Book{vtkBook,
-  author    = "Will Schroeder and Ken Martin and Bill Lorensen",
-  title     = "The Visualization Toolkit (4th ed.)",
-  publisher = "Kitware",
-  year      = "2006",
-  isbn      = "978-1-930934-19-1",
-}
-```