Add examples about recursive tag family

[hibetterheyj]

Dear developers.

I am working on a drone-related application, which requires some tags with a long detection range. Therefore, I would like to seek advice from you on how to generate suitable tags with a recursive style. I would appreciate it if you could provide some pre-generated ones.

Best regards~

[dleporis]

Similar problem here

[seqwalt]

My steps for generating a recursive tag:

1. Download multiple tagCustom48h12 tags
2. Scale them up with convert in the terminal (I used 1000%), or use the provided tag_to_svg.py script to generate svg images.
3. Open a graphics editor (I used Inkscape), load all your edited tags, and embed them inside of each other recursively. Say you want to imbed tag B inside tag A. Tag A is 10x10 units, so tag B needs to be shrunk to 2x2 units, and placed in the center of tag A.
4. Export the resulting image.

I used a tag bundle provided by apriltag_ros to detect the recursive tag. I've attached a recursive tag I made, in which the tag IDs are 0 (outer), 1, and 2 (inner). Hope this helps!

[prayagk101]

@hibetterheyj @dleporis There is an ongoing project on recursive fiducial marker which might be of interest
https://github.com/astradyn/astratag