Fix typos in PBS 101-109

[deafiant]

I've found PBS while trying to learn about Chezmoi and I'm enjoying the info on Git. I'm fixing typos as I read & this is the first batch of suggested fixes. (I've added prev/next links to the Markdown files to help me navigate. You probably don't want this. [I had a quick look to see if I could add them to the Jekyll template but that is over my head at the moment.])

[podfeet]

@deafiant - this is terrific! I have always wanted a next/previous button at the bottom but never asked how it could be done. I love the idea and your implementation is even cooler with the titles so you know what the next/previous lesson is.

Can I ask for two things? Can you put the script in a scripts folder instead of in docs? It's a little confusing having it in the same folder as the pages themselves.

The other thing is could you split the typo commit from the index commit? That would make it much easier for us to accept the pull request when we're ready.

Thank you so much for this, I love it!

[podfeet]

In looking at the script we see one improvement required. I'd like to be able to run the script right before I publish. The last thing I do is add the links to the index. If I run the script now, it will keep adding the links at the bottom without checking to see if the link is already there.

The last installment also doesn't have a next (because there isn't one) so the script needs to check to see if there's a next and add it in.

We'll leave it to you on how to solve this.

[hepabolu]

@deafiant Thank you so much for your work, sorry it took so long to process the pull request. I've taken the liberty to split the PR into a commit with all the typos and another with an extended version of your script to generate the links.