Fix README local Maven install command

Switching from the maven to maven-publish plugin means users should use publishToMavenLocal to install jars into their local Maven cache.

Closes gh-10047

Author: eleftherias

README.adoc

@@ -43,7 +43,7 @@ git clone [email protected]:spring-projects/spring-security.git
 === Install all spring-\* jars into your local Maven cache
 [indent=0]
 ----
-./gradlew install
+./gradlew publishToMavenLocal
 ----
 
 === Compile and test; build all jars, distribution zips, and docs