Fix processing but of further_description from manual_input.csv and 'solar', 'solar-rooftop' description

[euronion]

Changes proposed in this Pull Request

• Fix source and further description for solar and solar-rooftop to indicate where these numbers are really coming from (not DEA TD) (h/t to @awongel for pointing out this issue)
• Fix a bug where further_description from manual_inputs.csv was not correctly parsed into the output files.

Checklist

• Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• Data source for new technologies is cleary stated.
• [n/a] Newly introduced dependencies are added to environment.yaml (if applicable).
• A note for the release notes doc/release_notes.rst of the upcoming release is included.
• I consent to the release of this PR's code under the GPLv3 license.

[lisazeyen]

Thanks a lot @euronion !