README: Flesh out the intention and references, etc.

Signed-off-by: Ikey Doherty <ikey@thunderbird.net>

Author: ikeycode

README.md

@@ -1,5 +1,24 @@
 # Exchange Web Services
 
-This rust crate holds types that represent data structures and operations for
-the Exchange Web Services API, as well as the necessary infrastructure to
-serialize and deserialize them to/from XML.
+This repository contains the `ews-rs` Rust crate, home to a number of specialized
+data structures and scaffolding APIs to serialize and deserialize [EWS SOAP API](https://learn.microsoft.com/en-us/exchange/client-developer/web-service-reference/ews-reference-for-exchange)
+requests and responses in a more idiomatic fashion.
+
+Client libraries can be built atop this crate, as we explicitly focus on the protocol
+format rather than applications specifics such as socket negotiation or stream management.
+
+The reference implementation for this crate is the upcoming EWS protocol in [Thunderbird](https://thunderbird.net):
+
+ - `XPCOM` encapsulation: [ews_xpcom](https://hg.mozilla.org/comm-central/file/tip/rust/ews_xpcom)
+ - C++ protocol bridging: [ews](https://hg.mozilla.org/comm-central/file/tip/mailnews/protocols/ews)
+
+## Minimum Supported Rust Version
+
+The `MSRV` for `ews-rs` is currently: `1.62.1`
+
+Note that the use within `comm-central` may require a different MSRV than demonstrable by the code here.
+For further information please consult the [Rust Update Policy](https://firefox-source-docs.mozilla.org/writing-rust-code/update-policy.html#minimum-supported-rust-version)
+
+## License
+
+`ews-rs` is available under the terms of the [MPL-2.0](https://spdx.org/licenses/MPL-2.0.html) license.