adds key points that are related to frequently used commands

Adding How to add R packages

Rebase of (#186) Assorted minor fixes to spelling, whitespace, hyperlinks & sorting

Some commits from (lesson-example/186) Assorted minor fixes to spelling, whitespace, hyperlinks & sorting

https://cran.r-project.org/doc/manuals/r-patched/R-exts.html#Specifying-URLs

fix github meta data

Fix typos

Updating to handbook as canonical source for CoC

don't break words in code

Update repo_check.py with new GitHub labels

Delete 08-maintenance.md

This information is being migrated to the Carpentries Handbook:

- [Maintainer Onboarding Process](http://docs.carpentries.org/topic_folders/maintainers/maintainers.html#maintainer-onboarding)
- [Lesson Release Process and Schedule](http://docs.carpentries.org/topic_folders/lesson_development/lesson_release.html)
- [GitHub Issue Tags](http://docs.carpentries.org/topic_folders/maintainers/github_labels.html)

As @marwahaha said

> "master repository" feels overloaded,
> since typically "master" refers to a branch name.

We are going to use "originating repository".

Close #211

Close #217

Intends to fix issue 182

Fix source of typo #646

Specify release repo unambiguously

Link DOIs to preferred resolver