Default start directory in Ubuntu on WSL

refering to new installation guide for unix shell: https://github.com/carpentries/workshop-template/blob/gh-pages/_includes/install_instructions/shell.html

When using Ubuntu via WSL on Windows, the shell by default starts in the Linux home directory (`/home/`), not in the Windows home directory. This can cause confusion e.g. for a Library Carpentry with the shell-lesson folder, especially when participants are asked to place the shell-lesson folder on their Windows Desktop.

### Problem

If the folder is on the Windows Desktop, the path to access it is:

```
/mnt/c/Users//Desktop/shell-lesson
```

Instead of the simpler command from the lesson:

```
cd Desktop/shell-lesson
```

This mismatch may confuse beginners and lead to errors.

### Possible solutions

#### Pre-workshop setup

Ask learners to add the following line at the end of their ~/.bashrc so that their shell starts in the Windows home directory:

```
cd /mnt/c/Users/
```

I did it like this in my last workshop. In that case `cd` won't bring them back to the Windows Home directory, but therefore I did not change the Home path permanently and I did not run into errors later when installing conda-forge through WSL or setting an SSH key pair for the Git Lesson.

#### Adapt the lesson

Update the Shell lesson instructions to explain that on WSL, learners might need to either

use the full Windows path under /mnt/c/..., or

move the shell-lesson folder into their Ubuntu home (/home/) via the terminal before starting the exercises.

This clarification would prevent confusion and make the experience smoother for WSL users.

Read _includes/install_instructions/shell.html and compare its Desktop navigation example with the WSL paths described in the issue. Update the guidance so WSL learners know which path or setup applies, then verify that a beginner can locate shell-lesson from the instructions without ambiguity.

Written by the indexing model from the issue text.