Show aliases in specification reference

[jeromedalbert]

Fixes ruby/rubygems#7790.

Problem

add_dependency is not documented in the specification reference, but it is documented in the rubydoc documentation. Since the specification is generated from the Gem::Specification class, similarly to rubydoc, I think the specification should also mention add_dependency as an alias.

Solution

Change the documentation template to show aliases in the specification reference like so:

FYI there is currently only one alias, which is add_dependency.

Alternative solution

I mentioned in ruby/rubygems#7790 that add_dependency seems to be more prominent, so alternatively we could show it more prominently in the reference by making it have its own entry as done in my other branch here, where the end result would look like this. I can update the PR if this way is preferred.

[deivid-rodriguez]

Not totally sure about which one of your proposals is best, but both improve the current situation. I'd say let's at least add this and we can discuss adding a separate entry for aliases too, or even inverting this and calling add_runtime_dependency an alias of add_dependency, or using add_runtime_dependency in bundle gem generated template.

[jeromedalbert]

All good points @deivid-rodriguez, where do you recommend discussing this?

[deivid-rodriguez]

Let me merge this, and we can open a new issue in this repo, referencing this PR?

[jeromedalbert]

As I'm writing the issue, it looks like it is becoming more general and not just about the guides, so if you don't mind I'm going to create it in the rubygems/rubygems repo