How do I add a picture of my circuit or schematic to my question?
While editing your question (or answer), click on the icon that looks like a tiny mountain range, or hit control-G on your keyboard. You'll get a dialog that allows you to drag-and-drop an image, or enter a URL.
The image will be copied to imgur.com and a properly-formatted link to it inserted into your post.
For schematic diagrams specifically, you can also hit control-M on your keyboard to bring up the CircuitLab editing and simulation tool.