docs: fix lists display issue (#17911)
**Description:** Fix lists display issues in **Docs > Use Cases > Q&A
with RAG > Quickstart**.
In essence, this PR changes:
```markdown
Some paragraph.
- Item a.
- Item b.
```
to:
```markdown
Some paragraph.
- Item a.
- Item b.
```
There needs an extra empty line to make the list rendered properly.
FYI, the old version is displayed not properly as:
<img width="856" alt="image"
src="https://github.com/langchain-ai/langchain/assets/22856433/65202577-8ea2-47c6-b310-39bf42796fac">
- [x] **Lint and test**: Run `make format`, `make lint` and `make test`
from the root of the package(s) you've modified. See contribution
guidelines for more: https://python.langchain.com/docs/contributing/
Co-authored-by: Bagatur <baskaryan@gmail.com>
