Added information on how to add an image to OSM

[Themis3000]

Hi again! To compliment my last pull request (#78), I thought it might also be helpful to add a section about how to add images on OSM via wikimedia commons.

I personally think it's pretty important that eventually things transition to expecting images with every upload (for verifiability + public evidence of previous existence if it becomes legally relevant to a user). I don't think the discussion can be had if it should be required moving forward until there's support in the mobile app for images. Regardless, I think it's a good step to let users know how to do it on osm's editor. I marked the step as "optional" in the instructions.

Here's a screenshot of what I've added:

Admittedly, it's a little bit long. I tried to keep it sort of short, but perhaps it's cramming too much into one step?

Here's all of the source screenshots & affinity files, just in case anyone would like to tweak anything about the graphics I included: deflock-instructions.zip

Let me know if such a thing is desirable to merge or if you have any thoughts. Happy to make any tweaks to it if needed.

-Themis

[Themis3000]

Oh, and just to mention I did add more instructional graphics then was used. I thought it might be helpful for the future, just in case we want to add more micro steps in the future no one will have to go digging to find them. I can remove those unused images if you'd like though.