docs: Add Rego language (#18217)

Release Notes:

- N/A

---------

Signed-off-by: Charlie Egan <charlieegan3@users.noreply.github.com>
Co-authored-by: Charlie Egan <charlieegan3@users.noreply.github.com>
Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

docs/src/SUMMARY.md

@@ -93,6 +93,7 @@
 - [PureScript](./languages/purescript.md)
 - [Python](./languages/python.md)
 - [R](./languages/r.md)
+- [Rego](./languages/rego.md)
 - [ReStructuredText](./languages/rst.md)
 - [Racket](./languages/racket.md)
 - [Roc](./languages/roc.md)

docs/src/languages.md

@@ -45,6 +45,7 @@ Zed supports hundreds of programming languages and text formats. Some work out-o
 - [PureScript](./languages/purescript.md)
 - [Python](./languages/python.md)
 - [R](./languages/r.md)
+- [Rego](./languages/rego.md)
 - [ReStructuredText](./languages/rst.md)
 - [Racket](./languages/racket.md)
 - [Roc](./languages/roc.md)

docs/src/languages/rego.md

@@ -0,0 +1,38 @@
+# Rego
+
+Rego language support in Zed is provided by the community-maintained [Rego extension](https://github.com/StyraInc/zed-rego).
+
+- Tree Sitter: [FallenAngel97/tree-sitter-rego](https://github.com/FallenAngel97/tree-sitter-rego)
+- Language Server: [StyraInc/regal](https://github.com/StyraInc/regal)
+
+## Installation
+
+The extensions is largely based on the [Regal](https://docs.styra.com/regal/language-server) language server which should be installed to make use of the extension. Read the [getting started](https://docs.styra.com/regal#getting-started) instructions for more information.
+
+## Configuration
+
+The extension's behavior is configured in the `.regal/config.yaml` file. The following is an example configuration which disables the `todo-comment` rule, customizes the `line-length` rule, and ignores test files for the `opa-fmt` rule:
+
+```yaml
+rules:
+  style:
+    todo-comment:
+      # don't report on todo comments
+      level: ignore
+    line-length:
+      # custom rule configuration
+      max-line-length: 100
+      # warn on too long lines, but don't fail
+      level: warning
+    opa-fmt:
+      # not needed as error is the default, but
+      # being explicit won't hurt
+      level: error
+      # files can be ignored for any individual rule
+      # in this example, test files are ignored
+      ignore:
+        files:
+          - "*_test.rego"
+```
+
+Read Regal's [configuration documentation](https://docs.styra.com/regal#configuration) for more information.