gitignore: Ignore the sg_execution_times.rst file generated by Sphinx-Gallery (#3145)

Author: seisman

.gitignore

@@ -31,6 +31,8 @@ doc/gallery/
 doc/projections/
 doc/tutorials/
 doc/get_started/
+# doc/sg_execution_time.rst is auto-generated by Sphinx-Gallery
+doc/sg_execution_times.rst
 
 # Jupyter Notebook
 .ipynb_checkpoints/