Fix default file path

Fixed the location of the default file path to mirror the one mentioned
in the README. It now roughly adheres to the XDG home data location as
its default.

Added simple path validation for passed in file paths - will not see if
its readable/writable but simply look for the file's existence and error
out otherwise.

options.py

@@ -1,4 +1,5 @@
 import os
+import sys
 import argparse
 from dataclasses import dataclass, field
 from typing import List
@@ -6,8 +7,9 @@ from typing import List
 
 @dataclass
 class Options:
-    # can be changed
-    jrnl_fname: str = f"{os.path.expanduser('~')}/documents/records/todo.md"
+    jrnl_fname: str = field(
+        default_factory=lambda: f"{os.environ.get('XDG_DATA_HOME', os.environ.get('HOME'))}/jrnl/journal.txt"
+    )
     todo_block_title: str = "todotxt"
     dryrun: bool = False
     taskwarrior_log_completed: bool = True
@@ -36,6 +38,7 @@ def init():
     parse_cmdline_args(parser, opt)
     if opt.dryrun:
         dryrun_show_options(opt)
+    validate_opts(opt)
     return opt
 
 
@@ -94,3 +97,9 @@ def parse_cmdline_args(parser, options):
         options.todo_block_title = args.blocktitle
 
     return options
+
+
+def validate_opts(options):
+    if not os.path.isfile(options.jrnl_fname):
+        print(f"{options.jrnl_fname} does not seem to be a file. Aborting.")
+        sys.exit(1)