Add ecosystem guides (#3847)

* Add ecosystem guides

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docs/guides/install/add-dev.md

@@ -0,0 +1,26 @@
+---
+name: Add a development dependency
+---
+
+To add an npm package as a development dependency, use `bun add --development`.
+
+```sh
+$ bun add zod --development
+$ bun add zod -d # shorthand
+```
+
+---
+
+This will add the package to `devDependencies` in `package.json`.
+
+```json-diff
+{
+  "devDependencies": {
++   "zod": "^3.0.0"
+  }
+}
+```
+
+---
+
+See [Docs > Package manager](/docs/cli/install) for complete documentation of Bun's package manager.