add basic example for compiling upkr to a c library

c_library/Readme.md

@@ -0,0 +1,11 @@
+This is a simple example of compiling upkr to a library that can be linked in a
+c program. It consists of a small rust crate which implements the c api and
+compiles to a static library and a matching c header file. As is, the rust
+crate offers two simple functions to compress/uncompress data with the default
+upkr config.
+
+The provided makefile will only work on linux. Building the example upkr.c on
+other platforms is left as an exercise for the reader ;)
+
+On Windows you might have to make sure to install and use the correct rust
+toolchain version (mingw vs. msvc) to match your c compiler.