Fix spelling and grammar

Author: aldas

_fixture/certs/README.md

@@ -1,4 +1,4 @@
-To generate a valid certificate and private key use following command:
+To generate a valid certificate and private key use the following command:
 
 ```bash
 # In OpenSSL ≥ 1.1.1
@@ -7,7 +7,7 @@ openssl req -x509 -newkey rsa:4096 -sha256 -days 9999 -nodes \
   -addext "subjectAltName=DNS:localhost,IP:127.0.0.1,IP:::1"
 ```
 
-To check a certificate use following command:
+To check a certificate use the following command:
 ```bash
 openssl x509 -in cert.pem -text
 ```