More additions

[GreatEmerald]

A few more notes:

• It's not clear how to answer the question about the difference between ls -l etc. before they get to the section about finding help. Either we can move the help section higher, or add an extra note to run man ls as an explanation (I think it started off as something the students can try and find out by looking at the output, but the man page is very clear about it).
• Python interpreter is called python, but without Mamba, it's actually available only as python3.
• It is not clear that the hello world script is a script that should be copied and pasted into a file, rather than run from the terminal. Same goes for the big GDAL script, some students ended up just pasting the whole thing to the terminal.