binman: Update entry help for files-align

Regenerate the entry documentation, which step was missed when the
files-align feature was added.

Fixes: 6eb99326 ("binman: Support alignment of files")
Signed-off-by: NSimon Glass <sjg@chromium.org>

tools/binman/README.entries

@@ -302,6 +302,7 @@ Properties / Entry arguments:
     - files-compress: Compression algorithm to use:
         none: No compression
         lz4: Use lz4 compression (via 'lz4' command-line utility)
+    - files-align: Align each file to the given alignment
 
 This entry reads a number of files and places each in a separate sub-entry
 within this entry. To access these you need to enable device-tree updates