chore: Add an explanatory note about the OG split to top of README.md

[donaldguy]

This recreates #39 under a branch name which will hopefully satisfy the failed action

I became aware of the split here by virtue of my brew update producing:

…
==> Downloading https://formulae.brew.sh/api/cask.jws.json
aphera: Raw photo editing software
logseq-og: Privacy-first, open-source platform for knowledge sharing and management
…

and was curious enough to run brew home logseq-og and end up here. While I did see the "(file based)" in this repo's description, (as someone who hasn't been following dev of Logseq), I was unable to answer my immediate question of "As opposed to what?" in my first 3 attempts of:

1. looking at the README of this repo
2. navigating over to the other version's repo & looking at its description and README
3. looking at this repo's most recent release

(while I would have succeeded if I'd gone perhaps one further and looked at that repo's newest release, I in fact switched over to the different tact of seeing what the person who had contributed the formula/cask had said )

I think it is appropriate to include an easily locatable explanation to answer this question.

I was feeling generous this afternoon to jump through the various hoops to offer this PR (as my first contribution to Logseq) as one such option

---

Feel free to change the format of the callout to [!NOTE], etc. if you think it a better fit, etc.

[donaldguy]

A lighter weight option that may suffice (but only occurred to me during writing the above PR description… the first time) would be to set the repo url to https://logseq.io/p/e3YDyX5AYr or similar