Add .idea folder to .gitignore

.idea folder is where Project settings are stored with each specific
project as a set of xml files.
diff --git a/.gitignore b/.gitignore
index 09223fa..75a73a1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -99,3 +99,6 @@
 
 # Git generated files for conflicting
 *.orig
+
+# IDE specific folder for JetBrains IDEs
+.idea/