docs: add Leonardo Zizzamia to GDE resources

[Zizzamia]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[x] Documentation content changes
[ ] angular.io application / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

This adds Leonardo Zizzamia to the list of Angular GDEs on the Angular Docs page -> cc @StephenFluin

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[StephenFluin]

This should be 'GDE'

[Zizzamia]

Thank you @StephenFluin

[StephenFluin]

Can you squash these two commits?

https://twitter.com/stephenfluin/status/1009904095073718275

[brandonroberts]

Update git commit message to docs: add Leonardo Zizzamia to GDE resources

[brandonroberts]

@Zizzamia will you rebase on master and update the git commit message?

[googlebot]

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[googlebot]

CLAs look good, thanks!

[brandonroberts]

@Zizzamia will you rebase again to fix the merge conflict? Thanks.

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