Fix make and makefile in README.md files

That is

    sgit -e 's/Use make\( to compile\)/Use `make`\1/g' -e \
     's/makefile/Makefile/g'  '20[0-9][0-9]/README.md'

This way 'make' is formatted with a code block (or whatever the term is
in markdown terminology) and 'makefile' is changed to Makefile.

BTW: fun fact: Landon was part of the recommendation of naming Makefiles
Makefile instead of makefile which is shown in the man page make(1):

    Normally you should call your makefile either makefile or Makefile.
    (We recommend Makefile because it appears prominently near the
    beginning of a directory listing, right near other important files
    such as README.) The first name checked, GNUmakefile, is not
    recommended for most makefiles.  You should use this name if you
    have a makefile that is specific to GNU Make, and will not be
    understood by other versions of make.  If makefile is '-', the
    standard input is read.

2018/README.md

@@ -13,15 +13,15 @@ The primary IOCCC web site can be found at,
 
 >	<https://www.ioccc.org/>
 
-Use make to compile entries.  It is possible that on non-Unix / non-Linux
-systems the makefile needs to be changed.  See the Makefile for details.
+Use `make` to compile entries.  It is possible that on non-Unix / non-Linux
+systems the Makefile needs to be changed.  See the Makefile for details.
 
 Look at the source and try to figure out what the programs do, and run
 them with various inputs.  If you want to, look at the hints files for
 spoilers - this year we included most of the information included
 by the submitter.
 
-Read over the makefile for compile/build issues.  Your system may require
+Read over the Makefile for compile/build issues.  Your system may require
 certain changes (add or remove a library, add or remove a #define).
 
 Some C compilers are not quite as good as they should be.  If yours is