Update README and fix sample filter

README.md

@@ -1,2 +1,95 @@
 # gomilter
-Go Bindings for libmilter
+Go Bindings for Sendmail's libmilter
+
+Tested on Linux and FreeBSD
+
+## Installation
+
+The Sendmail header file libmilter/mfapi.h is required. For Redhat/CentOS, install the sendmail-devel package:
+```sh
+yum install sendmail-devel
+```
+
+Install the gomilter package:
+
+```sh
+go get github.com/leonrbaker/gomilter
+```
+
+##Usage
+
+The milter is implemented in a struct. Start by defining your own struct type and embeding the gomilter MilterRaw struct.
+
+```go
+type Mymilter struct {
+	gomilter.MilterRaw // Embed the basic functionality.
+}
+```
+
+Milter callbacks are added by implementing methods for the struct with matching predefined names.
+
+### Callbacks
+
+* Connect
+* Helo
+* EnvFrom
+* EnvRcpt
+* Header
+* Eoh
+* Body
+* Eom
+* Abort
+* Close
+
+Not all the callbacks need to be defined. The callbacks are explained on the milter.org site. Unfortunately the milter.org site has been shut down but it is still on [web.archive.org](http://web.archive.org/web/20150510034154/https://www.milter.org/developers/api/index)
+
+### Message Modification Functions
+
+* AddHeader
+* ChgHeader
+* InsHeader
+* ChgFrom
+* AddRcpt
+* AddRcpt_Par
+* DelRcpt
+* ReplaceBody
+
+### Other Message Handling Functions
+* progress
+
+### Startup
+
+The Socket field of the milter struct must be set. For example:
+```go
+mymilter.Socket = "unix:/var/gomilter/socket"
+```
+
+Control is handed over to the libmilter smfi_main function by calling the Run method and passing it a pointer to your milter struct
+```go
+gomilter.Run(mymilter)
+```
+
+The milter has a Stop method which calls the libmilter smfi_stop function.
+
+### Private Data
+
+libmilter is able to store private data for a connection. This data can be accessed from other functions and callbacks for the same connection. You can pass a pointer to any data structure to SetPriv. The data is retrieved with GetPriv
+```go
+t := T{1, 2, 3}
+m.SetPriv(ctx, &t)
+```
+Retrieve the data with
+```go
+var t T
+m.GetPriv(ctx, &t))
+```
+
+GetPriv should only be called once. If the private data is needed in another function or callback then call SetPriv again.
+
+## Sample Programs
+There are two sample programs included, samplefilter.go and samplefilter2.go
+
+##Other Libraries
+
+A usefull MIME parsing library is [go.enmime](https://github.com/jhillyerd/go.enmime)
+