Modify Gudni's notebook:

- use SolverLU in simpeg
- visualize fields

Add gitignore

.gitignore

@@ -0,0 +1,44 @@
+*.py[cod]
+
+# C extensions
+*.so
+
+# Folders
+docs/build/*
+
+# Packages
+*.egg
+*.egg-info
+dist
+build
+eggs
+parts
+bin
+var
+sdist
+develop-eggs
+.installed.cfg
+libgit
+lib64
+__pycache__
+
+# Installer logs
+pip-log.txt
+
+# Unit test / coverage reports
+.coverage
+.tox
+nosetests.xml
+
+# Translations
+*.mo
+
+# Mr Developer
+.mr.developer.cfg
+.project
+.pydevproject
+
+*.sublime-project
+*.sublime-workspace
+docs/_build/
+*.ipynb_checkpoints