Add ecosystem guides (#3847)

* Add ecosystem guides

* Update titles

* Rename stric

* Add unlink and fetch guides

* Add formdata guide

* Tweak title

* Moar

docs/guides/install/add-optional.md

@@ -0,0 +1,25 @@
+---
+name: Add an optional dependency
+---
+
+To add an npm package as a peer dependency, use the `--optional` flag.
+
+```sh
+$ bun add zod --optional
+```
+
+---
+
+This will add the package to `optionalDependencies` in `package.json`.
+
+```json-diff
+{
+  "optionalDependencies": {
++   "zod": "^3.0.0"
+  }
+}
+```
+
+---
+
+See [Docs > Package manager](/docs/cli/install) for complete documentation of Bun's package manager.