DOC: Small improvement to convert_objects doc
Fix small issues in convert_objects doc

[skip ci]

I think this is what I wanted (more indent of other stuff, not less of ipython blocks).  Does it seem right?
 other way. The ipython blocks can be put on the left margin (as this is an entire separate section)
 I think indentation is correct now.
 yep, better! only one line was still incorrect I think
 Thanks!
