Meaning of "fixed" vs "flexible" level is unclear

[tsmbland]

The documentation mentions that the "Level" parameter in the technodata and commodities files can be "fixed" or "flexible", but the meaning of these two options isn't adequately explained.

Sections to look at: 9.3.3 Techno-data (docs/inputs/technodata.rst) 9.3.5 Commodities (docs/inputs/commodities_io.rst)