Add some more inverter models

[laszlobortel]

I own a Sungrow SG2.5RS-S inverter:

• added all inverter models of the complete SG product series (8 types): https://www.pvo-int.com/wp-content/uploads/2022/03/EN-SG2.0_2.5_3.0RS-S_3.0_3.6_4.0_5.0_6.0RS-User-Manual-Ver15-202111.pdf
• reordered inverter models in increasing order of type code
• corrected the number of MPPTs for SG2.0RS-S (2 => 1)
• removed duplicate entry of 'SG8.0RT'
• corrected a typo in README.md
• corrected a typo in string.py