Created OTA over SCP (markdown)

OTA-over-SCP.md

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+How to setup and configure "OTA over SCP" upload for PlatformIO. The uploader pushes .bin files to remote OTA server using SCP. Images can be served to Sonoff-Tasmotas from there.
+
+# Configuration
+To upload .bin images to OTA server using SCP, one has to edit following lines under target environment:
+
+`[env:sonoff]`
+`...`
+`extra_scripts = pio/sftp-uploader.py`
+`upload_port = user@host:/path`
+
+upload_port should be modified to reflect user, host and path on the host where images should be uploaded.
+
+# Requirements
+SSH communication between the build server and OTA server should be pre-configured so that it doesn't require password (pre-shared keys).
+
+## Add the pre-shared key
+On a linux client machine type the following to generate the key:
+`ssh-keygen -t rsa -C "YOUR OWN KEY INFO"`
+Press enter three times (without any input).
+Copy the key to your ssh server:
+`ssh-copy-id -i ~/.ssh/id_rsa.pub USER@IPADRESS`
+You need to confirm this action. Use your server ssh password (one last time).
+_Optional reload the ssh service:_
+`sudo /etc/init.d/ssh restart`
+
+Easy compilation and upload can be performed from the icons at the laft side of the PlatformIO screen or use Ctrl + Alt + U to upload (will build if needed).
+
+More: https://github.com/arendst/Sonoff-Tasmota/pull/934