mimic-iv/buildmimic/sqlite/README: mention sqlalchemy requirement
mimic-iv/buildmimic/sqlite/README: mention sqlalchemy requirement

Without sqlalchemy installed, pandas throws the following error:

```
[...]
  File "/.../import.py", line 23, in <module>
    df.to_sql(tablename, CONNECTION_STRING)
[...]
  File "/.../python3.10/site-packages/pandas/io/sql.py", line 754, in pandasSQL_builder
    raise ImportError("Using URI string without sqlalchemy installed.")
ImportError: Using URI string without sqlalchemy installed.
```

MIT-LCP/mimic-code,MIT-LCP/mimic-code,MIT-LCP/mimic-code