Documentation issue: docs/developing-fuzzbench/custom_analysis_and_reports.md

I was trying to generate a simple report, following the command in the related documented. However, upon executing the command:
```
mkdir ~/my-report; cd ~/my-report
wget https://www.fuzzbench.com/reports/sample/data.csv.gz
PYTHONPATH= python3 analysis/generate_report.py \
[experiment_name] \
--report-dir ~/my-report \
--from-cached-data
```

I encountered the following issues:
- The postgresql service needs to be up and running and the postgresql password needs to be set. I am not sure if this is mentioned elsewhere though.
- The file provided for the `data.csv.gz` is missing the `crash_key` column, which is one of the expected ones; at the `data_utils.validate_data(experiment_df)` of the `generate_report.py`.

Eventually I executed the command as:
```
POSTGRES_PASSWORD= PYTHONPATH=fuzzbench python3 analysis/generate_report.py \
test-experiment \
--report-dir ~/my-report \
--from-cached-data
```

Upon adding a dummy column on the `data.csv.gz` and setting the password for the `postgres` user. Could you please update that documentation file?

Finally, there is a small mistake in the same document. The line `--report_type experimental` should be `--report-type experimental`.

Thank you.