gerrit_plugin: Fix deploy_env documentation

The deploy_env attribute was documented as "environment variables for
the deploy JAR", which is incorrect.

According to Bazel's java_binary documentation, deploy_env specifies a
list of java_binary targets that form the runtime environment loading
this binary (e.g. for plugins). Dependencies shared with these targets
are excluded from the runtime classpath and deploy jar.

Update the documentation to reflect the actual Bazel semantics.

Change-Id: I8210a1024f504f4ddd95eaa873cee15de15ea187

gerrit_plugin.bzl

diff --git a/gerrit_plugin.bzl b/gerrit_plugin.bzl
index 8e655b3..f1a8cbb 100644
--- a/gerrit_plugin.bzl
+++ b/gerrit_plugin.bzl
@@ -128,7 +128,9 @@
       dir_name: The directory name for the plugin, used in stamping. Defaults to `name`.
       license: Optional plugin-owned license file to package as `META-INF/LICENSE`.
       target_suffix: Suffix to append to the final plugin JAR name.
-      deploy_env: Environment variables for the deploy JAR.
+      deploy_env: List of java_binary targets representing the runtime/deployment
+        environment that will load this plugin. Dependencies shared with these
+        targets are excluded from this binary's runtime classpath and deploy jar.
       **kwargs: Additional arguments passed to the underlying `java_library` and `java_binary` rules.
 
     This rule creates a deployable .jar file for a Gerrit plugin."""