docs: guide - chaining actions

Signed-off-by: guillaume <guillaume.derouville@gmail.com>

docs/guides/1230-chain-actions.md

@@ -0,0 +1,54 @@
+---
+slug: /1230/chain-actions
+displayed_sidebar: europa
+---
+
+# How can I chain actions together ?
+
+Dependencies are materialized at runtime, when your Cue files are parsed and the corresponding DAG gets generated:
+
+```cue
+// Prerequisite action that runs when `test` is being called
+_dockerCLI: alpine.#Build & {
+    packages: {
+        bash: {}
+    }
+}
+
+// Main action
+foo: bash.#Run & {
+    input: _dockerCLI.output // <== CHAINING of action happening here
+    always: true
+    script: contents: #"""
+        echo "bonjour"
+        """#
+}
+```
+
+On above example, `_dockerCLI` gets executed first, as the corresponding DAG shows that it is required for the action `foo` to be processed.
+
+This is the `input-output` model: `foo`'s input is `_dockerCLI`'s output.
+
+We currently don't support explicit dependencies at the moment (one of our top priority). But, if you need one, here is how your can hack your way around it:
+
+```cue
+foo: bash.#Run & {
+    input: _dockerCLI.output
+    always: true
+    script: contents: #"""
+        echo "bonjour"
+        """#
+}
+
+// Main action
+bar: bash.#Run & {
+    input: _dockerCLI.output
+    always: true
+    script: contents: #"""
+        echo "bonjour"
+        """#
+    env: HACK: "\(test.success)" // <== HACK: CHAINING of action happening here
+}
+```
+
+`foo` and `bar` are similar actions. I don't want to rely on the `input-output` model but still want to force a dependency between them. The easiest way is to create an environment variable that relies on the other action's success