[Action View Overview Guide] Add note about Jbuilder

[cllns]

Currently, the Action View Overview talks about Builder, but doesn't mention Jbuilder.

Jbuilder is included in the default Gemfile (when running rails new app_name), so I think it deserves some mention in the guides. It's one of the only gems in there that doesn't get mentioned (the other s sdoc).

My impression is that JBuilder is currently used to render views more often than Builder.

Would be willing to expand this a little bit, but also reduce it to an INFO or TIP box.

Thoughts?

[rails-bot]

r? @senny

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[senny]

@cllns thank you 💛 The addition goes well with what we have on Builder already. Length and depth are fine. Readers looking for details should consult the Jbuilder docs.

[senny]

@cllns I changed the a tags to markdown markup in the merge commit (8516d76)

[cllns]

Awesome. thanks!