add WO_ANKI env var

[Madoshakalaka]

First there was a typo in the Running without Anki session in the Readme for linux systems. It's ~/.local/ instead of ~/local (as indicated in the code and as XDG default)

Second... I was trying to run it without anki and weirdly encountered errors as it seems to have found the wrong directory:

> python run_server.py
Initializing database. This make take a while...
(init_db) Adding entries from nhk16...
(make_nhk16_table) Cannot find entries file: /home/maa/Projects/local-audio-yomichan/plugin/user_files/nhk16_files/entries.json
(init_db) Adding entries from shinmeikai8...
(AJTJapaneseSource) Cannot find entries file: /home/maa/Projects/local-audio-yomichan/plugin/user_files/shinmeikai8_files/index.json
(init_db) Adding entries from forvo...
(init_db) Adding entries from jpod...
(init_db) Adding entries from jpod_alternate...
(init_db) Filling out JMdict forms...
Finished initializing database!
Running local audio server in debug mode...

I realized the detection logic is flawed, as I somehow have anki's aqt package installed as my system package, which is carried over even when I used python -m venv ./venv to create a virtual env for this repo. So the code would always think I'm inside anki and use the wrong directory.

I think introducing a seperate env var WO_ANKI is a good solution (open to better names). It's won't affect the current plugin users. And it won't affect those who already got it working standalone either because it means they don't have aqt installed.