docs: add minimal getting started example to quickstart

Author: hiijoshi

docs/quickstart.rst

@@ -6,3 +6,17 @@ Quickstart
 ==========
 
 This guide will get you started with borg-import.
+
+Getting started quickly
+-----------------------
+
+If you just want to try borg-import with minimal setup:
+
+::
+
+    git clone https://github.com/borgbackup/borg-import.git
+    cd borg-import
+    python -m venv env
+    source env/bin/activate
+    pip install -e .
+    borg-import --help