[SCREENSHOT] Keeps quiet when everything went well

Rationale: Before, sometimes the screenshot would be taken before
Archey's output was visible in the terminal. This delay ensures that
the terminal has had the chance to display the output before we take any
screenshot.

Additionally, this commit adds a success message detailing the
screenshot program used.

archey/screenshot.py

@@ -2,6 +2,7 @@
 
 import os
 import sys
+import time
 
 from contextlib import ExitStack
 from datetime import datetime
@@ -49,6 +50,15 @@ def take_screenshot(output_file=None):
         screenshot_tools['KDE-Spectacle'] = ['spectacle', '-b', '-o', output_file]
         screenshot_tools['Xfce4-Screenshooter'] = ['xfce4-screenshooter', '-f', '-s', output_dir]
 
+    # This part purposefully blocks so we wait a little bit before taking the screenshot.
+    # It prevents taking a screenshot before Archey's output has appeared.
+    taking_sc_fstring = '\rTaking screenshot in {:1d}...'
+    for time_remaining in range(3, 0, -1):
+        print(taking_sc_fstring.format(time_remaining), end='', flush=True)
+        time.sleep(1)
+    print('\r' + ' ' * len(taking_sc_fstring), end='\r', flush=True)
+    time.sleep(0.5)
+
     with ExitStack() as defer_stack:
         for screenshot_tool, screenshot_cmd in screenshot_tools.items():
             try: