Small corrections and cleaning on the LinuxGuide.md

[Neal-seal]

Description

• Removed fvwm from a list item for virtual machines.
• Removed kiwmi.
• Moved picom from the Wayland Compositors section to the more general Linux System section, particularly because the latter has a Window Manager index.
• Changed Linux-KVM description.

Context

• FVWM stands for F? Virtual Window Manager and its an X.Org/X11 window manager, it has nothing to do with virtual machines.
• Kiwmi hasn't been updated in 2+ years.
• Picom is a compositor for X.Org/X11, not for Wayland. That word has different meanings when it comes to those display protocols. On the former it refers to a software to be (optionally) used alongside a window manager to add some visual effects to it, like window animations, blur, rounded corners and so on. On the latter it refers to the window manger manager itself, which may or may not have said visual effects built directly into it. Since its a rather popular compositor for X i think its still worth keeping on the list.
• Since KVM is already part of the kernel and shipped in most distros by default, i thought that changing the description would be helpful for users to understand that.

Types of changes

• [X] Bad / Deleted sites removal
• [X] Grammar / Markdown fixes
• [ ] Content addition (sites, projects, tools, etc.)
• [ ] New Wiki section

Checklist:

• [X] I have read the contribution guide.
• [X] I have made sure to search before making any changes.
• [X] My code follows the code style of this project.