improve the documentation

README.md

@@ -4,8 +4,12 @@ This is a Go parser for `ssh_config` files. Importantly, this parser attempts
 to preserve comments in a given file, so you can manipulate a `ssh_config` file
 from a program, if your heart desires.
 
+It's designed to be used with the excellent
+[x/crypto/ssh](https://golang.org/x/crypto/ssh) package, which handles SSH
+negotiation but isn't very easy to configure.
+
 The `ssh_config` `Get()` and `GetStrict()` functions will attempt to read values
-from `$HOME/.ssh/config`, falling back to `/etc/ssh/ssh_config`. The first
+from `$HOME/.ssh/config` and fall back to `/etc/ssh/ssh_config`. The first
 argument is the host name to match on, and the second argument is the key you
 want to retrieve.
 
@@ -13,6 +17,10 @@ want to retrieve.
 port := ssh_config.Get("myhost", "Port")
 ```
 
+Some SSH arguments have default values - for example, the default value for
+`KeyboardAuthentication` is `"yes"`. If we can't find a value for the given
+Host/keyword pair, and a default exists for the keyword, we return it.
+
 Here's how you can manipulate an SSH config file, and then write it back.
 
 ```go
@@ -33,7 +41,7 @@ fmt.Println(cfg.String())
 
 Wherever possible we try to implement the specification as documented in
 the `ssh_config` manpage. Unimplemented features should be present in the
-[issues][issues] list.
+[issues][issues] list. Notably, the `Match` directive is currently unsupported.
 
 [issues]: https://github.com/kevinburke/ssh_config/issues