Add NGSI tenant/service preference documentation

Author: aarranz

README.md

@@ -62,6 +62,10 @@ Settings and Usage
   WireCloud 0.7.0+ in a experimental basis, future versions of WireCloud can
   change the way to use it making this option not funcional and requiring you to
   upgrade this operator.
+- **NGSI tenant/service**: Tenant/service to use when connecting to the context
+  broker. Must be a string of alphanumeric characters (lowercase) and the `_`
+  symbol. Maximum length is 50 characters. If empty, the default tenant will be
+  used
 - **NGSI entity types:** A comma separated list of entity types to use for
   filtering entities from the Orion Context broker. This field cannot be empty.
 - **Id pattern:** Id pattern for filtering entities. This preference can be

src/doc/userguide.md

@@ -33,6 +33,10 @@ Settings
   WireCloud 0.7.0+ in a experimental basis, future versions of WireCloud can
   change the way to use it making this option not funcional and requiring you to
   upgrade this operator.
+- **NGSI tenant/service**: Tenant/service to use when connecting to the context
+  broker. Must be a string of alphanumeric characters (lowercase) and the `_`
+  symbol. Maximum length is 50 characters. If empty, the default tenant will be
+  used
 - **NGSI entity types:** A comma separated list of entity types to use for
   filtering entities from the Orion Context broker. This field cannot be empty.
 - **Id pattern:** Id pattern for filtering entities. This preference can be