Update several README files to be consistent with the latest code (#426)

README.md

@@ -53,15 +53,15 @@ To build the virtual machine:
 - Install [Vagrant](https://vagrantup.com) and [VirtualBox](https://virtualbox.org)
 - Clone the repository
 - Before proceeding, ensure that your system has at least 25 Gbytes of free disk space, otherwise the installation can fail in unpredictable ways.
-- `cd vm`
+- `cd vm-ubuntu-20.04`
 - `vagrant up` - This step typically takes over 1 hour to complete, and requires a reliable Internet connection throughout.
-- When the machine reboots, you should have a graphical desktop machine with the required software pre-installed.  There are two user accounts on the VM, `vagrant` (password `vagrant`) and `p4` (password `p4`).  The account `p4` should be logged in when the VM boots up by default, and is the one you are expected to use.
+- When the machine reboots, you should have a graphical desktop machine with the required software pre-installed.  There are two user accounts on the VM, `vagrant` (password `vagrant`) and `p4` (password `p4`).  The account `p4` is the one you are expected to use.
 
 *Note*: Before running the `vagrant up` command, make sure you have enabled virtualization in your environment; otherwise you may get a "VT-x is disabled in the BIOS for both all CPU modes" error. Check [this](https://stackoverflow.com/questions/33304393/vt-x-is-disabled-in-the-bios-for-both-all-cpu-modes-verr-vmx-msr-all-vmx-disabl) for enabling it in virtualbox and/or BIOS for different system configurations.
 
 You will need the script to execute to completion before you can see the `p4` login on your virtual machine's GUI. In some cases, the `vagrant up` command brings up only the default `vagrant` login with the password `vagrant`. Dependencies may or may not have been installed for you to proceed with running P4 programs. Please refer the [existing issues](https://github.com/p4lang/tutorials/issues) to help fix your problem or create a new one if your specific problem isn't addressed there.
 
-To install dependencies by hand, please reference the [vm](./vm) installation scripts.
+To install dependencies by hand, please reference the [vm-ubuntu-20.04](./vm-ubuntu-20.04) installation scripts.
 They contain the dependencies, versions, and installation procedure.
 You should be able to run them directly on an Ubuntu 16.04 machine:
 - `sudo ./root-bootstrap.sh`

vm-ubuntu-20.04/README.md

@@ -14,12 +14,12 @@ new VM very often (a couple of times per year?).
 
 + Log in as user p4 (password p4)
 + Click "Upgrade" in the pop-up window asking if you want to upgrade
-  the system, if asked.  This will download the latest Linux Linux
-  kernel version released for Ubuntu 20.04, and other updated
-  packages.
+  the system, if asked.  This will download the latest Linux kernel
+  version released for Ubuntu 20.04, and other updated packages.
 + Reboot the system.
-+ Use `sudo apt purge <list of packages>` to remove older version of
-  Linux kernel, if the upgrade installed a newer one.
++ This is optional, but if you want to save a little disk space, use
+  `sudo apt purge <list of packages>` to remove older version of Linux
+  kernel, if the upgrade installed a newer one.
 + `sudo apt clean`
 
 + Log in as user p4 (password p4)
@@ -49,14 +49,6 @@ new VM very often (a couple of times per year?).
   + Sublime Text
   + Terminal
   + Wireshark
-+ cd tutorials
-  + `git remote add jafingerhut https://github.com/jafingerhut/tutorials`
-  + `git pull jafingerhut`
-  + `git checkout jafingerhut/add-2021-mar-vm-based-on-ubuntu-20.04`
-  + The above commands change to a branch that includes changes for
-    using Python3, and hopefully removes all traces of using Python2.
-    This is relatively new as of March 2021, and there may be bugs
-    remaining to be found.
 + Log off
 
 + Log in as user vagrant (password vagrant)

vm/README.md

@@ -0,0 +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.
+
+See the `vm-ubuntu-20.04` directory for similar scripts that can be
+used to create a VM image based on Ubuntu 20.04 Linux, and uses only
+Python3.