Update initialize-database.rst

[jmfreeman]

Remove ambiguity in the language as only MySQL and Postgres are supported backends.

---

^ Add meaningful description above

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[boring-cyborg]

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[XD-DENG]

SQLite should be mentioned given it's important for development/testing purpose.

Almost all new users start with SQLite (e.g. to test if the installation/setting-up is working). It will be weird to exclude it here.

Edit: what I meant is to mention SQLite (and highlight it's primarily for development purpose), to ensure consistent information. Otherwise people having quick looking at this may have the confusion "SQLite is not supported".

[potiuk]

Approved with the "SQLite" modification

[XD-DENG]

@potiuk I made some minor changes on top of your suggestion (add "as", and fix the trailing comma to period.)

[boring-cyborg]

Awesome work, congrats on your first merged pull request!

[XD-DENG]

Thanks @jmfreeman for the contribution. Hope you are ok with the changes that @potiuk and I have made.

[potiuk]

Seems like one-sentence changes are those that gets the most scrutiny :) cool stuff!

[potiuk]

And we have a new contributor ;) @jmfreeman ... Looking forward to more contributions !