shorten introductory slides to present only two technologies

The introductory presentation for [episode 1](https://smcclatchy.github.io/spatial-transcriptomics/introduction.html) needs to be shortened to present only one image-based and one sequence-based technology. The episode itself can still contain other examples, but the talk needs to be sped up. Feedback indicates that study design from [episode 2](https://smcclatchy.github.io/spatial-transcriptomics/data-and-study-design.html) was too long, however, it's likely that the introduction went on too long and that people might have become impatient by the time I got to study design. There were also more positive comments about the study design than there were negative comments. See attached sticky note and form feedback for details.
Also see the comments in these two final feedback forms.
[Just-right-Balanced-lecture-hands-on (4).pdf](https://drive.google.com/file/d/1hV6ADG1t_m1nCpfoxtl1tc2iwEZdGviz/view?usp=sharing)
[Just-right-Balanced-lecture-hands-on (2).pdf](https://drive.google.com/file/d/1wVaQedTb6xnxnTwwt-oOVPfXPaBOV2rd/view?usp=sharing)