contrib/vscode/: debugging with VS Code and gdb

The externalConsole=true setting is broken for many users (launching the
debugger with such setting results in VS Code waiting forever without
actually starting the debugger). Also, this setting is a matter of user
preference, and is arguably better set in a "launch" section in the
user-wide settings.json than hardcoded in our script. Remove the line to
use VS Code's default, or the user's setting.

Add useful links in contrib/vscode/README.md to help the user to
configure VS Code and how to use the debugging feature.

Helped-by: Matthieu Moy <Matthieu.Moy@univ-lyon1.fr>
Helped-by: Derrick Stolee <derrickstolee@github.com>
Co-authored-by: BRESSAT Jonathan <git.jonathan.bressat@gmail.com>
Signed-off-by: COGONI Guillaume <cogoni.guillaume@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/vscode/init.sh

@@ -271,7 +271,6 @@ cat >.vscode/launch.json.new <<EOF ||
             "stopAtEntry": false,
             "cwd": "\${workspaceFolder}",
             "environment": [],
-            "externalConsole": true,
             "MIMode": "gdb",
             "miDebuggerPath": "$GDBPATH",
             "setupCommands": [