Explain what to do if example commands fail

When following the FUSE troubleshooting steps, the docs say to do

```
> sudo modprobe -v fuse
```

but the author assumes this works, and does not explain how to proceed in case of a response of

```
modprobe: ERROR: ../libkmod/libkmod.c:586 kmod_search_moddep() could not open moddep file '/lib/modules/4.4.0-43-Microsoft/modules.dep.bin'
modprobe: FATAL: Module fuse not found in directory /lib/modules/4.4.0-43-Microsoft
```

As you may have suspected, this is the result when following your guide on Ubuntu as installed on WSL, [where unfortunately modprobe and kernel modules in general are not supported](https://github.com/microsoft/WSL/issues/1893). Up till this point, nothing in the docs has indicated that using WSL means AppImages will not work at all ever.

Suggestion to improve the docs would be to either indicate up front, e.g. as one of the linux flavours, that WSL does not support AppImages.

By extension, it would be nice if the guide for using an AppImage without fuse would explain which file to run after `--appimage-extract`, since I now have a directory full of files, many of them executable, but none clearly named after the program I want to run.