doc: update doc for vUART to hypervisor console switch key

Things changed since following commit
(c623e1112 debug: vuart: add guest break key support).

Tracked-On: #8583
Signed-off-by: Qiang Zhang <qiang4.zhang@intel.com>

doc/developer-guides/hld/hv-console.rst

@@ -70,10 +70,24 @@ Specifically:
    the hypervisor shell. Inputs to the physical UART will be
    redirected to the vUART starting from the next timer event.
 
--  The vUART is deactivated after a :kbd:`Ctrl` + :kbd:`Space` hotkey is received
-   from the physical UART. Inputs to the physical UART will be
-   handled by the hypervisor shell starting from the next timer
-   event.
+-  The vUART enters escaping mode after a BREAK character is received from
+   the physical UART. When in escaping mode, next received character will
+   be a command. After processing this command, the vUART exits the escaping
+   mode. So far, following escaping commands are supported:
+
+   - BREAK charater. If user sends break charater again in escaping mode,
+     one break charater will be sent to vUART.
+
+   - Character "e". This will deactive vUART. Inputs to the physical UART will
+     be handled by the hypervisor shell starting from the next timer event.
+
+   Other characters are not supported. The physical UART will prompt out an
+   "Unknown escaping key" message and the active vUART exits escaping mode.
+
+   Note that the BREAK character is a control character and different serial
+   terminals have different ways to send it, for example, `<Ctrl-A> + F`
+   in minicom, `<Ctrl-a> + <Ctrl-\>` in picocom, right click -> special
+   command -> break in putty serial terminal.
 
 The workflows are described as follows:
 

doc/user-guides/acrn-shell.rst

@@ -167,7 +167,9 @@ vm_console
 
 The ``vm_console <vm_id>`` command switches the ACRN's console to become the
 VM's console.
-Press :kbd:`Ctrl` + :kbd:`Alt` + :kbd:`Space` to return to the ACRN shell console.
+Send a BREAK character to enter escaping mode and a character e to return to
+the ACRN shell console. For details on how the hypervisor console works,
+refer to :ref:`hv-console`.
 
 vioapic
 =======

hypervisor/debug/shell_priv.h

@@ -73,7 +73,7 @@ struct shell {
 
 #define SHELL_CMD_VM_CONSOLE		"vm_console"
 #define SHELL_CMD_VM_CONSOLE_PARAM	"<vm id>"
-#define SHELL_CMD_VM_CONSOLE_HELP	"Switch to the VM's console. Use [Ctrl+Spacebar] to return to the ACRN shell "\
+#define SHELL_CMD_VM_CONSOLE_HELP	"Switch to the VM's console. Use 'BREAK + e' to return to the ACRN shell "\
 					"console"
 
 #define SHELL_CMD_INTERRUPT		"int"