Geckodriver error

Message: 'geckodriver' executable needs to be in PATH.
Made all steps from the instruction and tryed to configure path source, same error

```
Workspace in use: "/home/arterra/InstaPy"
Traceback (most recent call last):
File "/home/arterra/.local/lib/python3.9/site-packages/selenium/webdriver/common/service.py", line 71, in start
self.process = subprocess.Popen(cmd, env=self.env,
File "/usr/lib/python3.9/subprocess.py", line 951, in __init__
self._execute_child(args, executable, preexec_fn, close_fds,
File "/usr/lib/python3.9/subprocess.py", line 1823, in _execute_child
raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: 'geckodriver'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/home/arterra/insta.py", line 54, in
session = InstaPy(username=insta_username,
File "/home/arterra/.local/lib/python3.9/site-packages/instapy/instapy.py", line 330, in __init__
self.browser, err_msg = set_selenium_local_session(
File "/home/arterra/.local/lib/python3.9/site-packages/instapy/browser.py", line 123, in set_selenium_local_session
browser = webdriver.Firefox(
File "/home/arterra/.local/lib/python3.9/site-packages/selenium/webdriver/firefox/webdriver.py", line 174, in __init__
self.service.start()
File "/home/arterra/.local/lib/python3.9/site-packages/selenium/webdriver/common/service.py", line 81, in start
raise WebDriverException(
selenium.common.exceptions.WebDriverException: Message: 'geckodriver' executable needs to be in PATH.
```

Start by reviewing the setup instructions and reproducing the reported Firefox startup failure with geckodriver. Check whether the documented PATH configuration is sufficient; the issue is done when the instructions let a user start the browser without the reported WebDriverException.

由索引模型根据 Issue 内容生成。