Add build-depends to README.

1 files changed, 24 insertions, 4 deletions

diff --git a/README b/README
index fe698bed..f514c7a1 100644
--- a/README
+++ b/README
@@ -107,13 +107,25 @@ For chunks, use the following fields:
 
 For strata, use the following fields:
 
+* `build-depends`: a list of strings, each of which refers to another
+  stratum that the current stratum depends on. This list may be omitted
+  or empty if the stratum does not depend on anything else.
 * `sources`: a list of key/value mappings, where each mapping corresponds
   to a chunk to be included in the stratum; the mappings may use the
   following keys: `name` is the chunk's name (may be different from the
   morphology name), `repo` is the repository in which to find (defaults to
   chunk name), `ref` identifies the commit to use (typically a branch
   name, but any tree-ish git accepts is ok), and `morph` is the name
-  of the morphology to use; optional
+  of the morphology to use and is optional. In addition to these keys,
+  each of the sources may specify a list of build dependencies using the
+  `build-depends` field. This field may be omitted to make the source
+  depend on all other chunks that are listed earlier in the `sources`
+  list. The field may be an empty list to indicate that the chunk does 
+  not depend on anything else in the same stratum. To specify one ore 
+  more chunk dependencies, `build-depends` needs to be set to a list
+  that contains the names of chunks that the source depends on in the 
+  same stratum. These names correspond to the values of the `name` 
+  fields of the other sources.
 
 For systems, use the following fields:
 
@@ -154,15 +166,23 @@ Example stratum:
             {
                 "name": "linux-api-headers",
                 "repo": "linux",
-                "ref": "baserock/morph"
+                "ref": "baserock/morph",
+                "build-depends": []
             },
             {
                 "name": "eglibc",
-                "ref": "baserock/bootstrap"
+                "ref": "baserock/bootstrap",
+                "build-depends": [
+                  "linux-api-headers"
+                ]
             },
             {
                 "name": "busybox",
-                "ref": "baserock/bootstrap"
+                "ref": "baserock/bootstrap",
+                "build-depends": [
+                  "fhs-dirs",
+                  "linux-api-headers"
+                ]
             }
         ]
     }