[GH 2874] Fix category for deb and clairfy directory information in README for linux

[BaumiCoder]

Summary

Fix the category for deb installation. The abnormal category for deb was been added with f4e2d91 by @Willyfrog. The changes in the commit seems to be not related with the category so it was probably a mistake to set the category for deb at this point.

And some changes to clarify where the directory of the application can be found.

I did not "execute" or test my changes in any way. I have no glue how to build such a electron application. I hope someone can check it before it will be merged.

And about the Unittest topic: Is it even possible to check such things in a Unittest

Ticket Link

Closes #2874

Checklist

• read and understood our Contributing Guidelines
• completed Mattermost Contributor Agreement
• executed npm run lint:js for proper code formatting

Device Information

This PR was tested on:

Release Note

Set the category for the main menu correctly for installation with deb package.

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[devinbinnie]

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[BaumiCoder]

/check-cla

[devinbinnie]

Thanks for these updates @BaumiCoder!
Just tested and it looks like the app is showing under Internet on XFCE which is expected.