deploytool: Add README.md, migrate docs to it.

deploytool/api/deploy/config.proto

Index: deploytool/api/deploy/config.proto
diff --git a/deploytool/api/deploy/config.proto b/deploytool/api/deploy/config.proto
index 553d2fbf5182eb9e3b164b4b21b5c57b06b136ef..5bf506dc08457fed01def3a1dcac083b15a9c69f 100644
--- a/deploytool/api/deploy/config.proto
+++ b/deploytool/api/deploy/config.proto
@@ -9,48 +9,11 @@ package deploy;
 import "github.com/luci/luci-go/deploytool/api/deploy/checkout.proto";
 
 /**
- * The deployment configuration is a set of parameters composed from local and
- * source configuration files. Each configuration file is read as a text
- * protobuf in two stages:
+ * Layout defines the root directory of a deployment configuration.
  *
- * Local Stage
- * ============
- * First, the source and project layout configurations are loaded. These detail
- * the projects that are to be deployed and the source definitions for those
- * projects.
- *
- * Local configurations are located in subdirectories relative to a root
- * "layout.cfg" file:
- *
- * /layout.cfg
- * /sources/
- *   <source-group-name>/     (Defines a source group).
- *     <source-name>.cfg      (Defines a source within the source group).
- *
- * /applications/
- *   <application-name>.cfg   (Defines a application).
- *
- * /deployments/
- *   <deployment-name>.cfg    (Defines a deployment).
- *
- * Each "source" defines host repositories to check out with that source's name.
- * Sources can be pulled from a variety of places, and will be checked out into
- * uniquely-named staging directories.
- *
- * Each "application" defines a set of source-relative components that the
- * application is composed of. The components' definitions are located in the
- * deployment configuration area within their source.
- *
- * A "deployment" binds an "application" to a set of "sources" and
- * deployment-specific parameters (e.g., cloud project). A deployment's
- * configuration is composed of its application's components loaded from their
- * sources. Deployment operations are executed against deployments.
- *
- * Source Stage
- * ============
- * Each source referenced by the named application(s) will be checked out in a
- * staging area. Configurations referenced by the applications will then be
- * loaded from those sources to complete the deployment configuration.
+ * Each layout field has a default value, so an empty layout protobuf file is
+ * a valid layout. Each field may be overridden to suit your repository's
+ * structure, if needed.
  */
 message Layout {
   /**
@@ -87,7 +50,7 @@ message Layout {
  * "<source-name>.cfg". The source can be referenced internally by its full
  * source path, "<source-group-name>/<source-name>".
  *
- * If the source root contains a ".luci-deploytool.cfg" file, it will be read
+ * If the source root contains a "luci-deploy.cfg" file, it will be read
  * and interepreted as a "SourceLayout" message.
  */
 message Source {
@@ -124,7 +87,7 @@ message Source {
   /**
    * If true, this repository is allowed to run scripts:
    * - At source initialization time, the initialization scripts defined in
-   *   ".luci-deploytool.cfg" will be executed.
+   *   "/luci-deploy.cfg" will be executed.
    * - At build time, build scripts associated with a Component will
    *   be executed. Note that if the a Component declares a build script and `run_scripts` is not true,
    *   the build will fail.