docs: add alpha notice and update docs (#173)

* docs: add alpha notice

Signed-off-by: mikeee <hey@mike.ee>

* docs: bump rust required version

Signed-off-by: mikeee <hey@mike.ee>

* docs: add discord social channel

Signed-off-by: mikeee <hey@mike.ee>

* docs: fix missing brace

Signed-off-by: Mike Nguyen <hey@mike.ee>

---------

Signed-off-by: mikeee <hey@mike.ee>
Signed-off-by: Mike Nguyen <hey@mike.ee>

README.md

@@ -1,7 +1,8 @@
-# Dapr SDK for Rust
+# Dapr SDK for Rust (Alpha)
 
 [![Crates.io][crates-badge]][crates-url]
 [![Build Status][actions-badge]][actions-url]
+[![discord][discord-badge]][discord-url]
 [![License: Apache 2.0][apache-badge]][apache-url]
 [![FOSSA Status][fossa-badge]][fossa-url]
 
@@ -13,17 +14,36 @@
 [actions-url]: https://github.com/dapr/rust-sdk/actions?query=workflow%3Adapr-rust-sdk
 [fossa-badge]: https://app.fossa.com/api/projects/custom%2B162%2Fgithub.com%2Fdapr%2Frust-sdk.svg?type=shield
 [fossa-url]: https://app.fossa.com/projects/custom%2B162%2Fgithub.com%2Fdapr%2Frust-sdk?ref=badge_shield
-
-⚠ Work in Progress ⚠
+[discord-badge]: https://img.shields.io/discord/778680217417809931
+[discord-url]: https://discord.com/channels/778680217417809931/778680217417809934
 
 Dapr is a portable, event-driven, serverless runtime for building distributed applications across cloud and edge.
 
 - [dapr.io](https://dapr.io)
 - [@DaprDev](https://twitter.com/DaprDev)
 
+## Alpha
+
+This SDK is currently in Alpha. Work is underway to bring forward a stable
+release and will likely involve breaking changes.
+- Documentation is incomplete.
+- Not all building blocks are currently implemented.
+- There may be bugs.
+- The SDK does not have complete test coverage.
+
+The maintainers commit to resolving any issues that arise and bringing this SDK
+to a stable release. With this in mind, the SDK will follow the norms and
+conventions of a stable SDK so far as is possible.
+
+This SDK will be accounted for as a part of the release process. Support for 
+the latest runtime release is targeted but not guaranteed.
+
+The main tenet of development will be stability and functionality that improves
+resiliency.
+
 ## Prerequisites
 
-Ensure you have Rust version 1.40 or higher installed. If not, install Rust [here](https://www.rust-lang.org/tools/install).
+Ensure you have Rust version 1.56 or higher installed. If not, install Rust [here](https://www.rust-lang.org/tools/install).
 
 You will also need to install [protoc](https://github.com/protocolbuffers/protobuf#protobuf-compiler-installation).
 
@@ -77,3 +97,9 @@ By default, the script fetches the latest proto updates from the master branch o
 ```bash
 ./update-protos.sh -v v1.12.0
 ```
+
+### Contact Us
+Reach out with any questions you may have and we'll be sure to answer them as
+soon as possible!
+
+[![Discord Banner](https://discord.com/api/guilds/778680217417809931/widget.png?style=banner2)](https://aka.ms/dapr-discord)