Created Enabling Yubikey OTP authentication (markdown)

Enabling-Yubikey-OTP-authentication.md

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+To enable YubiKey authentication, you must set the `YUBICO_CLIENT_ID` and `YUBICO_SECRET_KEY` env variables.
+
+If `YUBICO_SERVER` is not specified, it will use the default YubiCloud servers. You can generate `YUBICO_CLIENT_ID` and `YUBICO_SECRET_KEY` for the default YubiCloud [here](https://upgrade.yubico.com/getapikey/).
+
+Note: In order to generate API keys or use a YubiKey with an OTP server, it must be registered. After configuring your key in the [YubiKey Personalization Tool](https://www.yubico.com/products/services-software/personalization-tools/use/), you can register it with the default servers [here](https://upload.yubico.com/).
+
+```sh
+docker run -d --name bitwarden \
+  -e YUBICO_CLIENT_ID=12345 \
+  -e YUBICO_SECRET_KEY=ABCDEABCDEABCDEABCDE= \
+  -v /bw-data/:/data/ \
+  -p 80:80 \
+  mprasil/bitwarden:latest
+```