binman: Move 'special properties' docs to README.entries

This information should be in the entry it relates to, not in the main
README. Move it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/README.entries b/tools/binman/README.entries
index c6e7b22..041e777 100644
--- a/tools/binman/README.entries
+++ b/tools/binman/README.entries
@@ -524,6 +524,9 @@
 
 Properties / Entry arguments:
     - filename: Filename of u-boot-nodtb.dtb (default 'u-boot-nodtb.dtb')
+    - optional-ucode: boolean property to make microcode optional. If the
+        u-boot.bin image does not include microcode, no error will
+        be generated.
 
 See Entry_u_boot_ucode for full details of the three entries involved in
 this process. This entry updates U-Boot with the offset and size of the
@@ -543,7 +546,7 @@
     - kernelkey: Name of the kernel key to use (inside keydir)
     - preamble-flags: Value of the vboot preamble flags (typically 0)
 
-Chromium OS  signs the read-write firmware and kernel, writing the signature
+Chromium OS signs the read-write firmware and kernel, writing the signature
 in this block. This allows U-Boot to verify that the next firmware stage
 and kernel are genuine.