Update README.md

2-farm/lessons/6-keep-your-plant-secure/README.md

@@ -148,7 +148,7 @@ After the connection, all data sent to the IoT Hub from the device, or to the de
 
 ### X.509 certificates
 
-When you are using an asymmetric encryption with a public/private key pair, you need to provide your public key to anyone who wants to send you data. The problem is, how can the recipient of your key be sure it's actually your public key, not someone else pretending to be you? Instead of providing a key, you can instead provide your public key inside a certificate that has been verified by a trusted third party, called an X.509 certificate.
+When you are using asymmetric encryption with a public/private key pair, you need to provide your public key to anyone who wants to send you data. The problem is, how can the recipient of your key be sure it's actually your public key, not someone else pretending to be you? Instead of providing a key, you can instead provide your public key inside a certificate that has been verified by a trusted third party, called an X.509 certificate.
 
 X.509 certificates are digital documents that contain the public key part of the public/private key pair. They are usually issued by one of a number of trusted organizations called [Certification authorities](https://wikipedia.org/wiki/Certificate_authority) (CAs), and digitally signed by the CA to indicate the key is valid and comes from you. You trust the certificate and that the public key is from who the certificate says it is from, because you trust the CA, similar to how you would trust a passport or driving license because you trust the country issuing it. Certificates cost money, so you can also 'self-sign', that is create a certificate yourself that is signed by you, for testing purposes.