Documentation (#401)

* updated documentation/screenshots, let seated-recenter show in all modes, fixed default value of brigthness

* fixed formatting

* changed PTT to System

* added comma to documentation

src/res/qml/PlayspacePage.qml

@@ -502,7 +502,7 @@ MyStackViewPage {
                 MyPushButton {
                     id: spaceSeatedRecenter
                     Layout.preferredWidth: 250
-                    visible: false
+                    visible: true
                     text: "Seated Recenter"
                     onClicked: {
                         MoveCenterTabController.sendSeatedRecenter()
@@ -539,7 +539,7 @@ MyStackViewPage {
 
             } else if (MoveCenterTabController.trackingUniverse === 1) {
                 spaceModeText.text = "Standing"
-                spaceSeatedRecenter.visible = false
+                spaceSeatedRecenter.visible = true
                 offsetsGroupBox.visible = true
                 rotationGroupBox.visible = true
                 resetButtonRow.visible = true