Add install section to README; add make check note.

[libtap] / INSTALL

To install libtap on a unix-like system:

    $ make
    $ make check
    $ make install

Note that `make check` runs Perl unit-tests, which require the
Test::Differences module from CPAN; if you run them, make sure to install it.
To compile with gcc -ansi, run

    $ make ANSI=1

On Windows, the library can be created by first setting up
the correct development environment variables. Usually this
is done by running vcvars32.bat included in the visual studio
distribution. You should also install gnu make which can be
found at http://gnuwin32.sourceforge.net/packages/make.htm.
And you should have perl to run the tests although this isnt
absolutely necessary. Once this is done, you should be able to
run the following:

    > make -f Makefile.win
    > make check

Alternatively, you might want to use the visual studio project file
included by Alexander Kahl (e-user).

If you want to use it directly in another project, you can copy tap.c
and tap.h there and it shouldn't have a problem compiling.

    $ ls
    tap.c tap.h test.c
    $ cat test.c
    #include "tap.h"
    int main () {
        plan(1);
        ok(50 + 5, "foo %s", "bar");
        done_testing();
    }
    $ gcc test.c tap.c
    $ a.out
    1..1
    ok 1 - foo bar