vyos_command Document ANSIBLE_VYOS_TERMINAL_LENGTH (#5676)

* Update documentation for vyos_command

Add information on new environment variable added in #18546.
Add note on command that should not be run via Ansible.

* White space changes

Two spaces after period.

lib/ansible/modules/network/vyos/vyos_command.py

@@ -28,6 +28,10 @@ description:
     to validate key parameters before returning successfully.  If the
     conditional statements are not met in the wait period, the task
     fails.
+  - Certain C(show) commands in VyOS produce many lines of output and
+    use a custom pager that can cause this module to hang.  If the
+    value of the environment variable C(ANSIBLE_VYOS_TERMINAL_LENGTH)
+    is not set, the default number of 10000 is used.
 extends_documentation_fragment: vyos
 options:
   commands:
@@ -75,6 +79,10 @@ options:
         trying the command again.
     required: false
     default: 1
+
+notes:
+  - Running C(show system boot-messages all) will cause the module to hang since
+    VyOS is using a custom pager setting to display the output of that command.
 """
 
 EXAMPLES = """