`get_version` when using `archinstall` as python module instead of from pacman

[h8d13]

Traceback (most recent call last):                                                                                                                                   
    File "<frozen runpy>", line 198, in _run_module_as_main                                                                                                            
    File "<frozen runpy>", line 88, in _run_code                                                                                                                           
    File "/home/root/archinstoo/archinstall/__main__.py", line 3, in <module>                                                                                  
      from archinstall.main import main                                                                                                                                    
    File "/home/root/archinstoo/archinstall/main.py", line 11, in <module>                                                                                       
      from archinstall.lib.args import arch_config_handler                                                                                                             
    File "/home/root/archinstoo/archinstall/lib/args.py", line 560, in <module>                                                                              
      arch_config_handler: ArchConfigHandler = ArchConfigHandler()                                                                                                     
                                               ~~~~~~~~~~~~~~~~~^^                                                                                                     
    File "/home/root/archinstoo/archinstall/lib/args.py", line 258, in __init__                                                                              
      self._parser: ArgumentParser = self._define_arguments()                                                                                                          
                                     ~~~~~~~~~~~~~~~~~~~~~~^^                                                                                                          
    File "/home/root/archinstoo/archinstall/lib/args.py", line 304, in _define_arguments                                                                     
      version='%(prog)s ' + self._get_version(),                                                                                                                       
              ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~                                                                                                                        
  TypeError: can only concatenate str (not "NoneType") to str   

So from the read me we now promote this way of using it but it we also enforce this

	def _get_version(self) -> str:
		try:
			return version('archinstall')
		except Exception:
			return 'Archinstall version not found'

Which for obvious reasons would not exist since user used the git clone method (example on tarballs or minimal ISOs or from existing system).