* Clarify what IAQ is
Since standards are only for companies that lack a marketing department, I clarified some of the documentation around Bosch's definition of what IAQ means in their universe. There is a lot here and it was taken from their datasheet directly that I provided a link to anyway. I just wanted to include the important stuff to save people from surprises because like me they didn't bother to follow the links. I can remove the b-VOC stuff if it's too much noise, but I thought it clarified to the users what it might be measuring for. I also changed `2` to `₂` in `CO2` for the non-code snippets soothe the emotional damage incurred from doing too many school papers in LaTeX.
* fix table
* addded: BME680 IAQ Class
* fixed: yaml layout
* fixed: some iaq values has result in an error
* Update bme680_bsec.rst
* Update bme680_bsec.rst
Co-authored-by: H. Árkosi Róbert <robreg@zsurob.hu>
