binman: Support compressed entries

Add support for compressing blob entries. This can help reduce image sizes
for many types of data. It requires that the firmware be able to
decompress the data at run-time.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/README b/tools/binman/README
index 10dfe57..d687194 100644
--- a/tools/binman/README
+++ b/tools/binman/README
@@ -593,6 +593,22 @@
 of each entry.
 
 
+Compression
+-----------
+
+Binman support compression for 'blob' entries (those of type 'blob' and
+derivatives). To enable this for an entry, add a 'compression' property:
+
+    blob {
+        filename = "datafile";
+        compression = "lz4";
+    };
+
+The entry will then contain the compressed data, using the 'lz4' compression
+algorithm. Currently this is the only one that is supported.
+
+
+
 Map files
 ---------