Additions for "Getting started with QGIS" page

[ioalexei]

1. To emphasise the point about the relevance of QGIS being open source, can link to (or show) github.com/qgis/qgis where all the code is viewable.

2. This might be a good place to mention QGIS community / support channels: https://qgis.org/en/site/forusers/support.html#support

[ioalexei]

3. Could be useful to have a "Why QGIS?" section? e.g. why are we teaching QGIS and not ArcGIS?
4. Here might be a good place to clarify the pros and cons of being "constantly changing" and explain why there is a stable version
5. In the interface section, mention the * in the title bar means the project is unsaved

[ioalexei]

6. Could explain to people how to understand the warning icon and hover over it to view the text of the warning (this caused some confusion in the training)

[enauj]

@ioalexei which warning icon do you mean?

[ioalexei]

the yellow triangle that shows up next to some settings to indicate a warning message - e.g. like this:
https://www.qgistutorials.com/en/_images/417.png

When we ran the training, people were confused by the error and didn't know you could hover over it show text explaining the warning/error

[enauj]

I fixed the points in this issue.
Can i get some feedback if it's good like this?
Thanks

[ioalexei]

Thanks @enauj looks good to me