gitignore configuration for Mesh projects

Hey Lukas!

Yes, "Temp" directory is safe to add to gitignore.

Currently we don't provide an exhaustive "template" of a gitignore for unity projects using Mesh Toolkit, because some auto-generated files may be useful to version control in some cases: for example auto-generated thumbnails can be version controlled to capture evolution of the scene over time, but it is not essential to do so.

However here we have gitignore for our sample projects which filters out some of auto-generated files (e.g. Temp directories): https://github.com/microsoft/Mesh-Toolkit-Unity/blob/main/.gitignore