Phase 1 documentation update

docs/conf.py

docs/img/DC_compensation_pulses.png

docs/img/Drawings.pptx

docs/img/IQ_gain_error.png

docs/img/IQ_mixing.png

docs/img/IQ_offset_error.png

docs/img/bias_T.png

docs/img/bias_T_block_pulse.png

docs/img/bias_T_sequence.png

docs/img/ideal_modulation.png

docs/img/long_pulses.png

docs/img/long_pulses_with_compensation.png

docs/img/real_modulation.png

docs/index.rst

docs/installation.rst

docs/introduction.rst

docs/signals/attenuation.rst

docs/signals/bias_T.rst

docs/signals/cross_capacitance.rst

docs/signals/delays.rst