Fix instructions how to build the plugin with external dependencies

* The file that needs to be overridden is external_plugin_deps.bzl
  (not external_plugins_deps.bzl)
* The symbolic link plugins/external_plugin_deps.bzl must point to
  supermanifest/external_plugin_deps.bzl (not
  plugins/supermanifest/external_plugin_deps.bzl because this will
  resolve to plugins/plugins/supermanifest/external_plugin_deps.bzl
  which doesn't exist).

Change-Id: Ie1fced59dd0c6027388f0aba96b74f91a27ab63f
Signed-off-by: Edwin Kempin <ekempin@google.com>

java/Documentation/build.md

diff --git a/java/Documentation/build.md b/java/Documentation/build.md
index a447703..49a3e6d 100644
--- a/java/Documentation/build.md
+++ b/java/Documentation/build.md
@@ -11,12 +11,12 @@
 $ git clone https://....  plugins/supermanifest
 ```
 
-2. This plugin has external dependencies. We need to tell gerrit 
-   about it overwriting the external_plugins_deps.bzl:
+2. This plugin has external dependencies. We need to tell gerrit
+   about it overwriting the external_plugin_deps.bzl:
 
 ```bash
-rm plugins/external_plugins_deps.bzl
-ln -s  plugins/supermanifest/external_plugins_deps.bzl plugins/external_plugins_deps.bzl
+rm plugins/external_plugin_deps.bzl
+ln -s  supermanifest/external_plugin_deps.bzl plugins/external_plugin_deps.bzl
 ```
 
 3. Now it should build with