Add support for auto-detetcing OS heading for progress

This patch removes the cognitive overhead of having to manually set your
OS heading, --with-heading="Foo OS vX.YY".  As of this patch, Finit by
default extracts PRETTY_NAME from /etc/os-release.  It is now possible
to also disable the heading entirely using --without-heading

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

doc/build.md

@@ -83,8 +83,7 @@ Then configure, build and install:
 ```shell
 $ ./configure --prefix=/usr                 --exec-prefix=         \
               --sysconfdir=/etc             --localstatedir=/var   \
-			  --with-keventd                --with-watchdog        \
-              --with-heading="Alpine Linux" --with-hostname=alpine
+			  --with-keventd                --with-watchdog
 $ make
 .
 .