contrib: add a script to initialize VS Code configuration

contrib: add a script to initialize VS Code configuration

VS Code is a lightweight but powerful source code editor which runs on
your desktop and is available for Windows, macOS and Linux. Among other
languages, it has support for C/C++ via an extension, which offers to
not only build and debug the code, but also Intellisense, i.e.
code-aware completion and similar niceties.

This patch adds a script that helps set up the environment to work
effectively with VS Code: simply run the Unix shell script
contrib/vscode/init.sh, which creates the relevant files, and open the
top level folder of Git's source code in VS Code.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>