docs(spring-sdk): small fixes to Quickstart (#1267)

Rephrase inheritance description.

Fix CustomerEntity src path.

Fix typos.

docs/src/modules/spring/pages/quickstart/cr-value-entity-spring.adoc

@@ -57,16 +57,16 @@ The `Customer` API is defined by the `CustomerEntity`.
 Create a class names `CustomerEntity` in package `customer.api`.
 
 [source,java,indent=0]
-.src/main/java/customer/api/Address.java
+.src/main/java/customer/api/CustomerEntity.java
 ----
 include::example$spring-customer-registry-quickstart/src/main/java/customer/api/CustomerEntity.java[tag=customer]
 ----
 <1> Each Entity needs a unique logical type name. This must be unique per Kalix service.
 <2> The entity needs to be address by a unique identifier. The `@EntityKey` declares the name of the path variable that Kalix should use as unique identifier.
 <3> The `@RequestMapping` defines the base path to access the entity. Note that the `\{customer_id\}` matches the value of `@EntityKey`.
-<4> `CustomerEntity` must implement Kalix' `ValueEntity`
+<4> `CustomerEntity` must inherit from `kalix.javasdk.valueentity.ValueEntity`.
 <5> Each API method must be exposed as a REST endpoint using Spring's REST annotations.
-<6> The implementation instruct Kalix to persist the state `customer`
+<6> The implementation instructs Kalix to persist the state `customer`.
 <7> After persisting, Kalix is instructed to return the String 'Ok'.