Add support for Bazel in Gerrit tree build

Also add build instructions.

Change-Id: Ic3addbfdf9a0ba97d37261934576b3d64e14e489
diff --git a/BUILD b/BUILD
new file mode 100644
index 0000000..239b00f
--- /dev/null
+++ b/BUILD
@@ -0,0 +1,13 @@
+load("//tools/bzl:plugin.bzl", "gerrit_plugin")
+
+gerrit_plugin(
+    name = "project-download-commands",
+    srcs = glob(["src/main/java/**/*.java"]),
+    resources = glob(["src/main/resources/**/*"]),
+    manifest_entries = [
+        "Gerrit-PluginName: project-download-commands",
+        "Gerrit-Module: com.googlesource.gerrit.plugins.download.command.project.Module",
+        "Implementation-Title: Project download command plugin",
+        "Implementation-URL: https://gerrit-review.googlesource.com/#/admin/projects/plugins/project-download-commands",
+    ],
+)
diff --git a/src/main/resources/Documentation/build.md b/src/main/resources/Documentation/build.md
new file mode 100644
index 0000000..9e32d1d
--- /dev/null
+++ b/src/main/resources/Documentation/build.md
@@ -0,0 +1,35 @@
+Build
+=====
+
+This plugin is built using Bazel.
+Only the Gerrit in-tree build is supported.
+
+Clone or link this plugin to the plugins directory of Gerrit's source
+tree.
+
+```
+  git clone https://gerrit.googlesource.com/gerrit
+  git clone https://gerrit.googlesource.com/plugins/@PLUGIN@
+  cd gerrit/plugins
+  ln -s ../../@PLUGIN@ .
+```
+
+From Gerrit source tree issue the command:
+
+```
+  bazel build plugins/@PLUGIN@
+```
+
+The output is created in
+
+```
+  bazel-genfiles/plugins/@PLUGIN@/@PLUGIN@.jar
+```
+
+This project can be imported into the Eclipse IDE.
+Add the plugin name to the `CUSTOM_PLUGINS` set in
+Gerrit core in `tools/bzl/plugins.bzl`, and execute:
+
+```
+  ./tools/eclipse/project.py
+```