session 2: line 282 - use confidence intervals

[jayware9]

use confidence interval instead of +/- 1 s.d.? e.g. +/-1.96*sd(apps) / sqrt(n())

decision: +/- sd is easier and we aren't teaching a course on statistics. could add a note explaining we have simplified this bit and CI could be done in a similar manner

https://github.com/DataScienceScotland/intro_to_r/blob/17b78f13c38c16da9f22902a802a29f426d58f68/session2/intro_to_R_session2_incomplete.Rmd#L282

[irisoren-sg]

This has not been an issue when delivering the training, But a note to explain choice of SD could be added in future