[NUCLEO_F302R8] Add LSE configuration for RTC

[bcostm]

No description provided.

[bogdanm]

For some reason, your last 3 or 4 pull requests contain a very weird looking history of previous commits. I'm going to accept this one, but in the future I recommend one of the following:

1. merge code from our main repository to your repository before modifying code and issing a pull request
2. if that doesn't work, something has likely happened with your local repository, so I recommend making a fresh clone of our repository and work from that (there are other things to try, but this is probably the quickest one).

Thanks,
Bogdan

[PrzemekWirkus]

Maybe using git pull --rebase would help?

Some delivery like this should be on top of the current code:

git pull
... add your changes
git add X Y Z
...
git commit -m ""Added X Y Z"
...
git pull --rebase

... Your changes on top of current code

[bogdanm]

That would help, yes, but we're fine with simply merging (in my experience, rebase (or rather the way git does rebase) tends to confuse people). Still, we should aim to minimize the mess created by all these merges.