Update documentation around redirects

[kelson42]

... and aliases

[benoit74]

E.g. https://wiki.openzim.org/wiki/ZIM_Redirect_Vs_Alias

[veloman-yunkan]

I wonder if we should maintain documentation for libzim in two different places (openzim wiki and documentation in the libzim repository that is made available via readthedocs). Do you want me to incorporate https://wiki.openzim.org/wiki/ZIM_Redirect_Vs_Alias into the RTD version?

[kelson42]

Separation of duty is clear to me:

• libzim RTD gathers the necessary to deal with the libzim
• openzim.org is about the spec, tye tooling around the spec, and we also use it to document ZIM creation processes within Kiwix

There is clearly a bit of overlap, but I don't think the libzim documentation should start to paraphrase in detail the spec.

Still unsure about https://wiki.openzim.org/wiki/ZIM_Redirect_Vs_Alias...