docs: Serialization.jl should recommend a specific file extension #58544
Description
The current page for Serialization.jl doesn't recommend any specific file extension as a best practice/community convention: https://docs.julialang.org/en/v1/stdlib/Serialization/. I think it should make a recommendation for this. Scrolling the page I had no clue what to pick for it; I looked through some other packages and code examples to see that the community convention is .jls.
Related to original discussion in #7909.