Clarify the licenses for the icons

[manphiz]

I was trying to working on the Debian packaging of dap-mode and noticed that the files under icons directory are presumably derived from some external repositories:

• icons/vscode presumably from [1] which is under CC BY 4.0
• icons/eclipse presumably from [2] which is under EPL-1.0

It looks like they have different license from dap-mode which is under GPL-3+. Will you consider clarifying the license under those directories to be clearer?

[1] https://github.com/microsoft/vscode-icons
[2] https://github.com/eclipse-platform/eclipse.platform.images