Configure: change all references to INSTALL to INSTALL.md

Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/11657)

Configure

diff --git a/Configure b/Configure
index 48ebe4e..4a23d26 100755
--- a/Configure
+++ b/Configure
@@ -21,7 +21,7 @@
 use OpenSSL::Glob;
 use OpenSSL::Template;
 
-# see INSTALL for instructions.
+# see INSTALL.md for instructions.
 
 my $orig_death_handler = $SIG{__DIE__};
 $SIG{__DIE__} = \&death_handler;
@@ -1136,7 +1136,8 @@
 application.
 
 Please read the 'Note on random number generation' section in the
-INSTALL instructions and the RAND_DRBG(7) manual page for more details.
+INSTALL.md instructions and the RAND_DRBG(7) manual page for more
+details.
 ============================== WARNING ===============================
 
 _____
@@ -2616,7 +2617,7 @@
 
 The library could not be configured for supporting multi-threaded
 applications as the compiler options required on this system are not known.
-See file INSTALL for details if you need multi-threading.
+See file INSTALL.md for details if you need multi-threading.
 EOF
 
 print <<"EOF" if ($no_shared_warn);
@@ -2641,7 +2642,7 @@
 ***       perl configdata.pm --dump                                ***
 ***                                                                ***
 ***   (If you are new to OpenSSL, you might want to consult the    ***
-***   'Troubleshooting' section in the INSTALL file first)         ***
+***   'Troubleshooting' section in the INSTALL.md file first)      ***
 ***                                                                ***
 **********************************************************************
 EOF
@@ -2661,8 +2662,8 @@
     my @message = ( <<"_____", @_ );
 
 Failure!  $build_file wasn't produced.
-Please read INSTALL and associated NOTES files.  You may also have to look over
-your available compiler tool chain or change your configuration.
+Please read INSTALL.md and associated NOTES files.  You may also have to
+look over your available compiler tool chain or change your configuration.
 
 _____