docs: Improve Kerberos docs slightly (#455)

* docs: Improve Kerberos docs slightly

* fix space

docs/modules/hdfs/pages/usage-guide/security.adoc

@@ -12,7 +12,7 @@ To configure HDFS to use Kerberos you first need to collect information about yo
 Additionally you need a service-user, which the secret-operator uses to create create principals for the HDFS services.
 
 === 2. Create Kerberos SecretClass
-Afterwards you need to enter all the needed information into a SecretClass, as described in  xref:home:secret-operator:secretclass.adoc#backend-kerberoskeytab[secret-operator documentation].
+Afterwards you need to enter all the needed information into a SecretClass, as described in xref:home:secret-operator:secretclass.adoc#backend-kerberoskeytab[secret-operator documentation].
 The following guide assumes you have named your SecretClass `kerberos-hdfs`.
 
 === 3. Configure HDFS to use SecretClass
@@ -33,7 +33,7 @@ The `kerberos.secretClass` is used to give HDFS the possibility to request keyta
 The `tlsSecretClass` is needed to request TLS certificates, used e.g. for the Web UIs.
 
 
-=== 4. Verify that Kerberos is used
+=== 4. Verify that Kerberos authentication is required
 Use `stackablectl stacklet list` to get the endpoints where the HDFS namenodes are reachable.
 Open the link (note that the namenode is now using https).
 You should see a Web UI similar to the following:
@@ -74,5 +74,5 @@ spec:
 ----
 
 == Wire encryption
-In case kerberos is enabled, `Privacy` mode is used for best security.
-Wire encryption without kerberos as well as https://hadoop.apache.org/docs/stable/hadoop-project-dist/hadoop-common/SecureMode.html#Data_confidentiality[other wire encryption modes] are *not* supported.
+In case Kerberos is enabled, `Privacy` mode is used for best security.
+Wire encryption without Kerberos as well as https://hadoop.apache.org/docs/stable/hadoop-project-dist/hadoop-common/SecureMode.html#Data_confidentiality[other wire encryption modes] are *not* supported.