README.md: Add build and install instructions

Closes: #7

Author: erikd

README.md

@@ -1,2 +1,30 @@
 # rust-accumulator
 An optimized rust lib for a POC vector commitment scheme over a BLS based PCS
+
+The recommended way to install this library/dependency is via Nix, but
+if you are stubborn and would prefer to do it manually, read on.
+
+## Build and Install
+
+This repo contains a `Makefile` with all the standard `Make` targets.
+The `Makefile` only builds the static library.
+
+When this library is used by other packages, `pkg-config` is used to 
+find the correct `CFLAGS` and `LIBS` settings so the `Makefile` also
+contains a `make pkgconfig` target.
+
+Assuming you have the `cargo` (Rust build tool) installed (installing
+`cargo` will probably pull in everything else needed) you only need to
+specify an `INSTALL` directory.
+
+It is sensible to have a user local install path for libraries.
+Something like `$HOME/Local` and to then set the following environment
+variable set:
+```
+PKG_CONFIG_PATH=$HOME/Local/lib/pkgconfig
+```
+
+Building an installing this Rust library is as simple as:
+```
+INSTALL=$HOME/Local make install
+```