Update readme files 2024 oct (#643)

* Move optional steps for testing VMs out of README.md file
This may help avoid new users being confused that they must follow
those instructions.

Signed-off-by: Andy Fingerhut <andy_fingerhut@alum.wustl.edu>

* Update README at top level and in all vm directories to point to Ubuntu 24.04
since that is the only one that is still tested regularly.

Signed-off-by: Andy Fingerhut <andy.fingerhut@gmail.com>

---------

Signed-off-by: Andy Fingerhut <andy_fingerhut@alum.wustl.edu>
Signed-off-by: Andy Fingerhut <andy.fingerhut@gmail.com>

Author: jafingerhut

README.md

@@ -106,11 +106,11 @@ virtual machine or install several dependencies.
 3. Navigate to the cloned directory :
 
    ```
-   cd vm-ubuntu-20.04
+   cd vm-ubuntu-24.04
    ```
 4. Start the virtual machine using Vagrant:
    ```
-   vagrant up
+   vagrant up dev
    ```
    *Note* : The time for this step depends on your computer and Internet speed. On a 2015 MacBook Pro with a 50 Mbps download speed, it took approximately 20 minutes. Ensure a stable Internet connection throughout the process.
 

vm-ubuntu-20.04/README.md

@@ -1,5 +1,15 @@
 # Creating the VM
 
+This directory is here only for historical reference.  The scripts
+here _might_ still be useful for creating a VM image based on Ubuntu
+20.04 Linux, but they are not regularly tested by anyone, so might not
+produce a working system.
+
+See the `vm-ubuntu-24.04` [directory](../vm-ubuntu-24.04) for similar
+scripts that can be used to create a VM image based on Ubuntu 24.04
+Linux.
+
+
 + Below are the steps to create a brand new VM using Vagrant:
   + Install [Vagrant](https://developer.hashicorp.com/vagrant/docs/installation) on your system if it's not already installed.
   + In a shell/terminal window, change to this `vm-ubuntu-20.04`

vm/README.md

@@ -1,12 +1,12 @@
 # Introduction
 
-This directory is still here only for historical reference.  The
-scripts here can be used to create a VM image based on Ubuntu 16.04
-Linux, but free support and updates for that version of Ubuntu Linux
-ended in April 2021.  The VM created by these scripts also rely upon
-and install Python2 versions of several Python libraries, which the
-latest version of the tutorials repository no longer uses.
+This directory is here only for historical reference.  The scripts
+here _might_ still be useful for creating a VM image based on Ubuntu
+16.04 Linux, but free support and updates for that version of Ubuntu
+Linux ended in April 2021.  The VM created by these scripts also rely
+upon and install Python2 versions of several Python libraries, which
+the latest version of the tutorials repository no longer uses.
 
-See the  `vm-ubuntu-20.04` [directory](../vm-ubuntu-20.04) for similar scripts that can be
-used to create a VM image based on Ubuntu 20.04 Linux, and uses only
-Python3.
+See the `vm-ubuntu-24.04` [directory](../vm-ubuntu-24.04) for similar
+scripts that can be used to create a VM image based on Ubuntu 24.04
+Linux, and uses only Python3.