Add electromagnetism summary

It contains a summary of topics 1 through 4.

Change-Id: Id41a440f77d5b3c2ae52a10c3db1b5314bc8d777
diff --git a/.gitignore b/.gitignore
index cb3bd63..4fe75d1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,6 +7,11 @@
 *.synctex.gz
 *.bbl
 *.blg
+*.idx
+*.ilg
+*.ind
+*.toc
+*.auxlock
 
 # Bibtex-specific files
 *.bcf