Improve debian control description

[alexmyczko]

This should not be longer than 80 characters/line. The last two lines belong to /usr/share/doc/code/README.Debian

Also it should not start with "Visual Studio Code is" but rather with "This is"
Please refer to the Debian Developer Manual.

This PR fixes #feel free to create this one, but that's the problem:

apt-cache show code
---8<---snip-snap
Description: Code editing. Redefined.
 Visual Studio Code is a new choice of tool that combines the simplicity of a co
de editor with what developers need for the core edit-build-debug cycle. See htt
ps://code.visualstudio.com/docs/setup/linux for installation instructions and FA
Q.
---snip-snap--->8---
>>>