docs(languages): Add initial csharp + rust docs (#2256)

Author: bryphe

docs/docs/languages/c-sharp.md

@@ -0,0 +1,33 @@
+---
+id: c-sharp
+title: C#
+sidebar_label: C#
+---
+
+Onivim supports C# via the [`muhammad-sammy.csharp`](https://open-vsx.org/extension/muhammad-sammy/csharp) extension:
+
+![c-sharp](https://user-images.githubusercontent.com/13532591/89577746-fcfad100-d7e5-11ea-9e96-afb1edf630e2.png)
+
+The following features are supported:
+- Code completion
+- Diagnostics
+- Go-to definition
+- Signature Help
+
+### Setup
+
+1) Ensure you have the latest version of the .NET Core tools: https://docs.microsoft.com/en-us/dotnet/core/install/
+
+2) Install the extension via the command-line:
+
+- `oni2 --install-extension muhammad-sammy.csharp`
+
+### Usage
+
+Once installed, run `oni2` in the your project's folder - for example: `oni2 /path/to/csharp-project`, and then open a C# file.
+
+The first time the extension activates, it will automatically download and install the OmniSharp server.
+
+After the extension installs required dependencies, you'll see a status bar icon showing the server status, as well as the current project:
+
+![status-bar](https://user-images.githubusercontent.com/13532591/89578393-ea34cc00-d7e6-11ea-8b66-7b2f15151dfb.png)

docs/docs/languages/rust.md

@@ -0,0 +1,34 @@
+---
+id: rust
+title: Rust
+sidebar_label: Rust
+---
+Onivim supports rust via the [`matklad.rust-analyzer`](https://open-vsx.org/extension/matklad/rust-analyzer) extension:
+
+![rust](https://user-images.githubusercontent.com/13532591/89589799-443f8c80-d7fb-11ea-9d95-c2a89c7c1204.gif)
+
+The following features are supported:
+
+- Code completion
+- Diagnostics
+- Go-to definition
+- Hover
+- Document highlights
+
+### Setup
+
+1) Ensure you have `rust` and `cargo` installed: https://www.rust-lang.org/learn/get-started
+
+2) Install the extension via the command-line:
+
+- `oni2 --install-extension matklad.rust-analyzer`
+
+### Usage
+
+Once installed, run `oni2` in the your project's folder - for example: `oni2 /path/to/rust-project`, and then open a `.rs` file
+
+The first time the extension activates, it may prompt you to download `rust-analyzer` binaries.
+
+### More Info
+
+- [Rust-Analyzer Documentation](https://rust-analyzer.github.io/manual.html#installation)

docs/website/sidebars.json

@@ -25,7 +25,9 @@
       "languages/python",
       "languages/go",
       "languages/java",
-      "languages/c"
+      "languages/c",
+      "languages/c-sharp",
+      "languages/rust"
     ],
     "For Developers": [
       "for-developers/architecture",