docs(prerequisites): update to Node.js v16

Updates the Node.js version installed by the prerequisite instructions
from v14 to v16, which is the latest LTS release.

The instructions for installing the Node Version Manager (NVM) have
also been updated for v0.39.0 (previously v0.38.0).

Change-Id: I85528b3906305914ba6169b4dc5aafcf5b36a339
Signed-off-by: Chris Kay <chris.kay@arm.com>
diff --git a/docs/getting_started/prerequisites.rst b/docs/getting_started/prerequisites.rst
index f45193a..ee30128 100644
--- a/docs/getting_started/prerequisites.rst
+++ b/docs/getting_started/prerequisites.rst
@@ -75,7 +75,7 @@
    The standard software package used for debugging software on Arm development
    platforms and |FVP| models.
 
-- Node.js >= 14
+- Node.js >= 16
 
    Highly recommended, and necessary in order to install and use the packaged
    Git hooks and helper tools. Without these tools you will need to rely on the
@@ -98,13 +98,13 @@
     sudo apt install device-tree-compiler
 
 Additionally, to install an up-to-date version of Node.js, you can use the `Node
-Version Manager`_ to install a version of your choosing (we recommend 14, but
+Version Manager`_ to install a version of your choosing (we recommend 16, but
 later LTS versions might offer a more stable experience):
 
 .. code:: shell
 
-    curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.38.0/install.sh | "$SHELL"
-    exec "$SHELL" -ic "nvm install 14; exec $SHELL"
+    curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.0/install.sh | "$SHELL"
+    exec "$SHELL" -ic "nvm install 16; exec $SHELL"
 
 .. _Node Version Manager: https://github.com/nvm-sh/nvm#install--update-script