Adding more prominent grid editor docs (#1731)

The grid editor is a powerful feature, and not easy
to discover or featured in the docs. This adds
an intriguing figure (from our fftf isothermal repo)
up front so people can see what they're missing
and go looking for the feature.

Along the way, I noticed that all png files were
ignored across the repo. Since we use png images
in our documentation, it's important that we do not
blanket ignore such files. I struggled for a while
to find out why my png wasn't showing up in the options
to stage! If we have build artifacts that are ending
up in commits then I suggest we clean those out
or be more precise with the ignoring.

.gitignore

@@ -13,7 +13,6 @@ bin/*
 /bin
 dist/
 dist-*/
-*.png
 doc/_build
 doc/user/tutorials
 doc/tutorials/anl-afci-177*
@@ -59,7 +58,6 @@ venv*/
 **/.coverage*
 **/logs/*
 *.ascii
-*.png
 
 # Misc. exclusions
 *.html

armi/utils/gridEditor.py

@@ -21,6 +21,11 @@
 
     $ python -m armi grids
 
+If you have an existing set of input files, pass in the blueprints input file
+as the first argument and the system will load up the associated grid, e.g.::
+
+    $ python -m armi grids FFTF-blueprints.yaml
+
 
 **Known Issues**
 

doc/user/inputs.rst

@@ -1043,6 +1043,15 @@ Example grid definitions are shown below::
 .. tip:: We have gone through some effort to allow both pin and core grid definitions to share this
     input and it may improve in the future.
 
+You may set up some kinds of grids (e.g. 1/3 and full core hex or Cartesian core
+loadings) using our interactive graphical grid editor described more in
+:py:mod:`armi.utils.gridEditor`.
+
+.. figure:: /.static/gridEditor.png
+    :align: center
+
+    An example of the Grid Editor being used on a FFTF input file
+
 .. _custom-isotopics:
 
 Custom Isotopics