README: replace reference to boards.cfg

boards.cfg is not delivered with the U-Boot source. So it is preferable to
look at configs/*_defconfig to identify available deconfigs.

Fix a typo.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/README b/README
index 19dae14..7ebf9f5 100644
--- a/README
+++ b/README
@@ -3203,9 +3203,9 @@
 	make NAME_defconfig
 
 where "NAME_defconfig" is the name of one of the existing configu-
-rations; see boards.cfg for supported names.
+rations; see configs/*_defconfig for supported names.
 
-Note: for some board special configuration names may exist; check if
+Note: for some boards special configuration names may exist; check if
       additional information is available from the board vendor; for
       instance, the TQM823L systems are available without (standard)
       or with LCD support. You can select such additional "features"