Edit README

- Add build and installation instructions

README.md

@@ -12,6 +12,65 @@ Currently the milter does nothing but filling a logfile :)
 
 Please be patient.
 
+## Build
+
+Make sure that you have a toolchain for Rust installed. 
+
+Building:
+```
+$ git clone https://gitlab.com/husk-project/husk-milter.git
+$ cd husk-milter
+$ cargo build --release
+```
+
+This creates the binary `./target/release/husk`.
+
+## Installation
+
+To use with `postfix`:
+
+- configure husk, there is an example configuration file in `./config/config.toml`.
+
+    ```
+    #
+    # Husk config file
+    #
+    connection = "localhost:3000"
+
+    logfile_config = "./config/log4rs.yml"
+    ```
+    
+    Husk uses `log4rs` for logging. There is an example configuration in the
+    `./config` subdirectory as well.
+
+- Configure `postfix`:
+    
+    Make sure that the `main.cf` configuration file contains a line like:
+    ```
+    smtpd_milters = inet:localhost:3000
+    ```
+    `smtpd_milters` is used to register milters with postfix, there might be 
+    more than one. The string `inet:localhost:3000` corresponds to the 
+    `connection` setting in `config.toml`.
+
+- Start the milter:
+    
+    Assuming you are in the root directory of the project:
+
+    ```
+    $ ./target/release/husk ./config/config.toml
+    ```
+
+- Restart postfix:
+
+    In case you are using systemd:
+    ```
+    # systemctl restart postfix.services
+    ```
+
+- Send a mail and check the logfile.
+
+
 ## Funding
 
 This project is funded through the [NGI0 Commons Fund](https://nlnet.nl/core), a fund established by [NLnet](https://nlnet.nl/).