Adding Google App engine installation with composer instructions

[nalinbhardwaj]

Adds php.ini file instructions to both files USE_CASES.md and TROUBLESHOOTING.md

Fixes #423

@thinkingserious please review.

[SendGridDX]

All committers have signed the CLA.

[thinkingserious]

@nalinbhardwaj

We have not been able to merge your Pull Request, but because you are awesome - we wanted to make sure you could still get a SendGrid Hacktoberfest shirt.

Please go fill out our swag form before Nov 5th and we will send the shirt! (We know that you might have tried this before and it didn’t work, sorry about that!)

You have till Nov 5th to fill out this form in order to get the Hacktoberfest shirt!

Thank you for contributing during Hacktoberfest! We hope to see you in the repos soon! Just so you know, we always give away a SendGrid shirt for your first ever non-Hacktoberfest PR that gets merged.

[nalinbhardwaj]

@thinkingserious , thanks a lot, but I already filled this form for a PR on the docs repository, I don’t need to fill it again right?

Thanks for the swag though!

[thinkingserious]

@nalinbhardwaj,

No, you don't need to fill it out again. Sorry for the duplicate request, we are just trying to make sure we don't miss anyone :)

[m1guelpf]

👍 Good work

[thinkingserious]

Hello @nalinbhardwaj,

Thanks again for the PR!

We appreciate your contribution and look forward to continued collaboration. Thanks!

Team SendGrid DX