Update Chapter 8 - Using Git

[dvirlar2]

• [x] Include a step-by-step for finding the PAT
• [x] Suggest setting PAT for 90 days
• [x] Suggest setting PAT for specific settings
• [x] Include the cache --timeout function, and explain the number is in seconds, and that the seconds must be greater than or equal to 90 days. If it's shorter, the user will have to set a new PAT because RStudio will no longer have the cached PAT.
• [x] Edit format of git commands in section 8.3. Right now they appear on one line in the bookdown; move them to two lines

[dvirlar2]

• [x] Need to edit the format a little so there's more of a line break between paragraphs, code chunks, and images.