Update landing page now that AutoValue requires Java 8.

It has since cl/597954833 (in January, so it was [released in May](https://github.com/google/auto/releases/tag/auto-value-1.11.0)), but we didn't update this page.

Also, while in the area, bump a Javadoc link to point to a more recent version.

RELNOTES=n/a
PiperOrigin-RevId: 705183923

README.md

@@ -25,7 +25,7 @@ Save time.  Save code.  Save sanity.
 
     [![Maven Central](https://img.shields.io/maven-central/v/com.google.auto.service/auto-service.svg)](https://mvnrepository.com/artifact/com.google.auto.service/auto-service)
 
-  * [AutoValue] - Immutable [value-type] code generation for Java 7+.
+  * [AutoValue] - Immutable [value-type] code generation for Java 8+.
 
     [![Maven Central](https://img.shields.io/maven-central/v/com.google.auto.value/auto-value.svg)](https://mvnrepository.com/artifact/com.google.auto.value/auto-value)
 
@@ -56,4 +56,4 @@ Save time.  Save code.  Save sanity.
 
 [java]: https://en.wikipedia.org/wiki/Java_(programming_language)
 [value-type]: http://en.wikipedia.org/wiki/Value_object
-[`ServiceLoader`]: http://docs.oracle.com/javase/7/docs/api/java/util/ServiceLoader.html
+[`ServiceLoader`]: https://docs.oracle.com/en/java/javase/23/docs/api/java.base/java/util/ServiceLoader.html