[Draft] Include instructions about renaming images

[annavik]

Currently, we require trap images to include timestamp in the filename. This makes it possible for us to do fast indexing of files, which is helpful when reading a large amount of images from a remote storage.

For the AMI systems, images include timestamp in the filename by default and users don't have to worry about it. For other cameras however, this is often not the case. For users, this means images have to be renamed before being uploaded.

We provide a Python utility to automate this process. In this PR, we include some instructions on how to install and use this utility.

[annavik]

@mihow I put this together based on our notes from helping Ariane. Maybe you can test and refine the instructions if you will do the same with Santiago? I also hope we can make a short video about this and include later on :)