Update Readme/Documentation

[tobiasschuerg]

Documentation is quite outdated

• With Adds support for MH-Z14B and small additional features #46 new parameters were added which should be documented

MH-Z-CO2-Sensors/MHZ.cpp

Lines 285 to 288 in c83ba47

	void MHZ::setBypassCheck(boolean isBypassPreheatingCheck, boolean isBypassResponseTimeCheck) {
	_isBypassPreheatingCheck = isBypassPreheatingCheck;
	_isBypassResponseTimeCheck = isBypassResponseTimeCheck;
	}

• Added devices should be added to README

• Preheating shoud also be documented