docs: Patching docs about LanguageTool versions, and adding a precision in an error message about it

Author: mdevolde

README.md

@@ -270,7 +270,7 @@ into where the ``language_tool_python`` package resides.
 
 ### LanguageTool Version
 
-As of April 2020, `language_tool_python` was forked from `language-check` and no longer supports LanguageTool versions lower than 4.0.
+LanguageTool versions under 6.0 are no longer downloadable from the LanguageTool website. If you need to use an older version, you can download it from the [LanguageTool GitHub tags page](https://github.com/languagetool-org/languagetool/tags) and build it yourself.
 
 ### Acknowledgements
 

language_tool_python/download_lt.py

@@ -132,7 +132,7 @@ def http_get(url: str, out_file: IO[bytes], proxies: Optional[Dict[str, str]] =
     content_length = req.headers.get('Content-Length')
     total = int(content_length) if content_length is not None else None
     if req.status_code == 404:
-        raise PathError(f'Could not find at URL {url}. The given version may not exist.')
+        raise PathError(f'Could not find at URL {url}. The given version may not exist or is no longer available.')
     version = re.search(r'(\d+\.\d+)', url).group(1)
     progress = tqdm.tqdm(unit="B", unit_scale=True, total=total,
                          desc=f'Downloading LanguageTool {version}')