Docs restructuring in preparation for descriptions on tools usage.

docs/source/index.rst

@@ -19,6 +19,13 @@ gprMax User Guide
     geometry_snapshots
     output
 
+.. toctree::
+    :maxdepth: 2
+    :caption: Tools
+
+    plotting
+    helper
+
 .. toctree::
     :maxdepth: 2
     :caption: Advanced topics
@@ -27,7 +34,7 @@ gprMax User Guide
 
 .. toctree::
     :maxdepth: 2
-    :caption: Help and Support
+    :caption: Support
 
     examples_2D
     examples_3D
@@ -38,5 +45,4 @@ gprMax User Guide
     :maxdepth: 2
     :caption: Appendices
 
-    app_waveforms
-    app_references
+    references