Adding stock recovery backup advice for OOS users

Change-Id: I2714d68f8cb7f10b92b91ed3f48baf26f5f316c4
diff --git a/_oneplus/oneplus8t.markdown b/_oneplus/oneplus8t.markdown
index 10f350e..4798bd8 100644
--- a/_oneplus/oneplus8t.markdown
+++ b/_oneplus/oneplus8t.markdown
@@ -27,7 +27,9 @@
 
 fastboot boot path/to/twrp.img
 
-This will temporarily boot TWRP on your device. Now, either copy the TWRP installer zip to the phone and flash it, or go into adb sideload option from the booted twrp and execute the following command:
+This will temporarily boot TWRP on your device.
+At this point - if OOS is installed - it's recommended to take a backup of the current recovery as it will need to be restored for incremental OTAs to install successfully.
+Now, either copy the TWRP installer zip to the phone and flash it, or go into adb sideload option from the booted twrp and execute the following command:
 
 adb sideload path/to/twrp-installer.zip