update alt text

Author: zingale

content/12-extensions/extensions-example.md

@@ -31,6 +31,7 @@ Here's the resulting image
 
 ```{image} test.png
 :align: center
+:alt: An image of the Mandelbrot set
 ```
 
 ## Python with explicit loops

content/git/github.md

@@ -13,6 +13,7 @@ on your github home page and click on the "+" icon and select "New repository":
 
 ```{image} github-new.png
 :align: center
+:alt: an image of a github profile homepage
 ```
 
 Now we give the repository a name.  Let's use our initials, followed
@@ -26,6 +27,7 @@ not be empty initially.
 
 ```{image} github-create.png
 :align: center
+:alt: The github webpage for "create a new repository"
 ```
 
 Our project is now found at: ``https://github.com/ [username]/ [reponame]``,
@@ -112,6 +114,7 @@ Now we can git clone this repo.  From the github project page, click on the
 
 ```{image} github-clone.png
 :align: center
+:alt: A github webpage for our class test repo, showing the "code" button selected
 ```
 
 Copy the string in the text box there and then on your command line clone

content/git/pull-requests.md

@@ -52,6 +52,7 @@ control that we can do with as we please.  Click on the "fork" button.
 
 ```{image} github-fork.png
 :align: center
+:alt: The github webpage for our test repo with the "fork" button circled
 ```
 
 It may ask you where you want the fork to live—you want it to live
@@ -64,6 +65,7 @@ Now click on the *code* button and copy the SSH location.
 
 ```{image} github-copy-ssh.png
 :align: center
+:alt: our fork of the class test repo github web page with the code button pressed
 ```
 
 We want to add this fork as a new remote:
@@ -86,12 +88,14 @@ Now we can do all *pull-request*.  Select "pull requests"
 
 ```{image} github-pr.png
 :align: center
+:alt: The github webpage of our fork of the class test repo
 ```
 
 Then click on the "New pull request" button, and you'll see something like:
 
 ```{image} github-pr2.png
 :align: center
+:alt: The github weboge showing a pull request, highlighting the difference between the fork and the upstream repo.
 ```
 
 This is showing that you are asking to merge the changes in your fork into the
@@ -112,6 +116,7 @@ The overall workflow that we did: fork, push to our fork, issue a PR, looks like
 ```{image} github-workflow.png
 :align: center
 :width: 80%
+:alt: a diagram showing our workflow between the github class repo, our local macine, and our fork.
 ```
 
 

content/git/version-control.md

@@ -123,6 +123,7 @@ Consider the figure below:
 
 ```{image} distributed_version_control.png
 :align: center
+:alt: A diagram showing a central server and 3 machines interacting with their local rrepos and the center server
 ```
 
 We see: