Update links and improve accessibility in Instructor Notes

Some links were outdated, and some link texts went against good
practice for accessibility (using the URL or obscure phrases like
"this" or "this page").

I have also reworded the point about whitespace differences to make it
a bit more logical.

Author: alex-ball

instructors/instructor-notes.md

@@ -14,7 +14,7 @@ Known problems that learners encounter:
 
 ## Making a handout
 
-To make a handout for this lesson, adapt/print from [https://librarycarpentry.org/lc-git/reference.html](https://librarycarpentry.org/lc-git/reference.html).
+To make a handout for this lesson, adapt/print from the [Reference page](https://librarycarpentry.org/lc-git/reference.html).
 
 ***
 
@@ -54,34 +54,34 @@ working in teams or not, because it is
 
 ## Teaching Notes
 
-- Resources for "splitting" your shell so that recent commands remain in view: [https://github.com/rgaiacs/swc-shell-split-window](https://github.com/rgaiacs/swc-shell-split-window).
+- Utility for "splitting" your shell so that recent commands remain in view: [Software Carpentry Shell Split Window](https://github.com/UCL-ARC/swc-shell-split-window).
 
 - Make sure the network is working *before* starting this lesson.
 
 - Drawings are particularly useful in this lesson: if you have a whiteboard,
-  use it to visualise and describe the [GitHub flow](https://guides.github.com/introduction/flow/).
+  use it to visualise and describe GitHub flow.
+  The [current documentation of GitHub flow](https://docs.github.com/en/get-started/using-github/github-flow) is text-heavy,
+  so it might be easier to draw inspiration from the interactive guide "[Understanding the GitHub flow](https://web.archive.org/web/20200728161719/https://guides.github.com/introduction/flow/)" from 2020.
 
 - Version control is usually not the first subject in a workshop,
   so get learners to create a GitHub account after the session before.
   Remind learners that the username and email they use for GitHub (and setup
   during Git configuration) will be viewable to the public by default.
   However, there are many reasons why a learner may not want their personal
   information viewable, and GitHub has [resources for keeping an email address
-  private](https://help.github.com/en/github/setting-up-and-managing-your-github-user-account/setting-your-commit-email-address).
+  private](https://docs.github.com/en/account-and-profile/how-tos/email-preferences/setting-your-commit-email-address).
 
-- If some learners are using Windows, there will inevitably be issues
-  merging files with different line endings.  (Even if everyone's on
-  some flavor of Unix, different editors may or may not add a
-  newline to the last line of a file.) Take a moment to explain
-  these issues, since learners will almost certainly trip over them
-  again.  If learners are running into line ending problems, GitHub
-  has a [page](https://help.github.com/en/articles/dealing-with-line-endings) that helps with troubleshooting.
+- It is likely that learners will run into issues when merging files due to whitespace differences.
+  For example, a text editor might automatically add a newline to the last line of a file, causing an unexpected difference.
+  Conflicts can also arise due to Windows using different line endings from other operating systems.
+  Take a moment to explain these issues, since learners will almost certainly trip over them again.
+  GitHub provides guidance on [how to configure Git to handle line endings](https://docs.github.com/en/get-started/git-basics/configuring-git-to-handle-line-endings).
 
-- We don't use a Git GUI in these notes because we haven't found one that
+- We don't use a Git GUI in this lesson because we haven't found one that
   installs easily and runs reliably on the three major operating systems, and
   because we want learners to understand what commands are being run.  That
   said, instructors should demo a GUI on their desktop at some point during
-  this lesson and point learners at [this page](https://git-scm.com/downloads/guis).
+  this lesson and point learners at the Git website's [list of available GUIs](https://git-scm.com/tools/guis).
 
 - Instructors should show learners graphical diff/merge tools like
   [DiffMerge](https://sourcegear.com/diffmerge/).
@@ -93,9 +93,6 @@ working in teams or not, because it is
 
 - Further resources:
 
-  - [git-it](https://github.com/jlord/git-it-electron#git-it-desktop-app) is a self-paced command-line Git demo,
-    with [git-it-electron](https://github.com/jlord/git-it-electron) its GitHub Desktop successor.
-  - Try GitHub's [resources to learn Git](https://try.github.io/) or Codeacademy's [Learn Git](https://www.codecademy.com/learn/learn-git).
+  - [Git-it](https://github.com/jlord/git-it-electron#git-it-desktop-app) is a self-paced Git demo that runs as an app on your computer.
+  - Try GitHub's [resources to learn Git](https://learn.github.com/) or Codecademy's [Learn Git & GitHub](https://www.codecademy.com/learn/learn-git).
   - For instructors, [the Git parable](https://tom.preston-werner.com/2009/05/19/the-git-parable.html) is useful background reading.
-
-