add usage info to README

README.md

@@ -1,5 +1,27 @@
 # gomap
 
-Go module for interfacing with [JMAP](https://jmap.io) servers
+Go module for interfacing with [JMAP](https://jmap.io) mail servers, such as [Fastmail](https://www.fastmail.com/).
 
-## 🚧 under construction 🚧
+## Usage
+
+To add the module to your project:
+
+```sh
+go get -u github.com/cwinters8/gomap
+```
+
+First, create a new mail client. You will need a session URL and a bearer token from your JMAP mail server. For Fastmail, the session URL is `https://api.fastmail.com/jmap/session`, and you can create an API token in [Settings > Privacy & Security > Integrations > API tokens](https://www.fastmail.com/settings/security/tokens). You will most likely need to give access to `Email` (for querying and reading email contents) and `Email submission` (for sending emails) when you create the token.
+
+```go
+mail, err := gomap.NewClient(
+  "https://api.fastmail.com/jmap/session",
+  os.Getenv("BEARER_TOKEN"),
+  gomap.DefaultDrafts,
+  gomap.DefaultSent,
+)
+if err != nil {
+  log.Fatal(err)
+}
+```
+
+Then you can use the client for your chosen operations. Check out the [examples](https://pkg.go.dev/github.com/cwinters8/gomap#pkg-examples) for full details on how to send and find emails.