Adding `README.md` related to `screenhack` files in previous commit.

diff --git a/screenhack/README.md b/screenhack/README.md
new file mode 100644 (file)
index 0000000..14da9d1
--- /dev/null
+++ b/screenhack/README.md
@@ -0,0 +1,36 @@
+Overview
+========
+
+The files in this directory comprise the `screenhack` API/library which is part
+of [xscreensaver](https://www.jwz.org/xscreensaver/). They are collected here
+in order to facilitate building the hacks contained in this repository without
+requiring an xscreensaver source tree and build system.
+
+
+Status
+======
+
+All files were extracted from the `xscreensaver-5.45.tar.gz` source tarball and
+remain unmodified.
+
+Since this directory only contains the files related to building X11 hacks
+utilizing the `screenhack` API, if you need the `xlockmore` API or OpenGL
+related files, either build your hack inside the xscreensaver source tree or
+copy the relevant files into this directory; the various makefiles are
+configured to automatically detect and compile them.
+
+
+Instructions
+============
+
+For an example of use, see the top-level directory `reference/` in this
+repository. It contains the `greynetic` hack, already configured to build
+against this `screenhack` library, as well as `README.hacking`, a guide to
+writing hacks against the `screenhack` library.
+
+Although all the hacks in this repo contain `#define`s hardcoded for FreeBSD,
+since all the `screenhack` files are unmodified, they all contain the various
+preprocessor trickery for building on other platforms. If you're having trouble
+figuring out the correct set of `#define`s for building on your system, try
+extracting the xscreensaver source, running `./configure`, and examining the
+`#define`s contained in the generated `config.h`.