add (a bit of) a readme

rust/dpll/README.md

@@ -0,0 +1,12 @@
# solve
**Warning**: *Don't use this, it's basically my "Hello World" in Rust
and looks and smells accordingly.  If you Know Things™ and want to tell
me how to do stuff better please do so, but don't expect to find pretty
things yet.  Maybe at some point in the future...*
That being said, this is me playing around with Rust and writing some
code related to constraint programming at the same time.
Currently there's an incomplete parser for CNFs in DIMAC format in
[./src/cnf.rs](./src/cnf.rs).