Refer to configure.ac instead of configure.in

Signed-off-by: Erik de Castro Lopo <erikd@mega-nerd.com>
diff --git a/README b/README
index 41ba136..1c0016e 100644
--- a/README
+++ b/README
@@ -93,7 +93,7 @@
 libFLAC has grown larger over time as more functionality has been
 included, but much of it may be unnecessary for a particular embedded
 implementation.  Unused parts may be pruned by some simple editing of
-configure.in and src/libFLAC/Makefile.am; the following dependency
+configure.ac and src/libFLAC/Makefile.am; the following dependency
 graph shows which modules may be pruned without breaking things
 further down:
 
@@ -174,7 +174,7 @@
 Use these if you have these packages but configure can't find them.
 
 If you want to build completely from scratch (i.e. starting with just
-configure.in and Makefile.am) you should be able to just run 'autogen.sh'
+configure.ac and Makefile.am) you should be able to just run 'autogen.sh'
 but make sure and read the comments in that file first.
 
 
@@ -245,6 +245,6 @@
 Building on Mac OS X
 ===============================================================================
 
-If you have Fink or a recent version of OS X with the proper autotooles,
+If you have Fink or a recent version of OS X with the proper autotools,
 the GNU flow above should work.  The Project Builder project has been
 deprecated but we are working on replacing it with an Xcode equivalent.