feat(2092): [2] Dropdown build parameters

docs/user-guide/configuration/parameters.md

@@ -9,14 +9,15 @@ toc:
       active: true
 ---
 ## Defining Parameters
-There are 2 ways to define parameters, you can see them both in the example below.
+There are 3 ways to define parameters, you can see them in the example below:
 
 ```yaml
 parameters:
     nameA: "value1"
     nameB:
         value: "value2"
         description: "description of nameB"
+    nameC: ["value1", "value2"]
 ```
 
 **Parameters** is a dictionary which expects `key:value` pairs.
@@ -37,6 +38,13 @@ parameters:
 
 These two examples above are equivalent.
 
+You can also define parameters in an array for drop down options. The first value in the array is picked up as default, e.g `value1` is selected as default in the example below:
+
+```yaml
+parameters:
+    nameA: ["value1", "value2"]
+```
+
 ## Example
 You can see a full screwdriver.yaml example below:
 ```yaml
@@ -48,13 +56,15 @@ parameters:
     az:
         value: "1"
         description: "default availability zone"
+    cluster: ["cluster1", "cluster2"]
 
 jobs:
     main:
         requires: [~pr, ~commit]
         steps:
             - step1: 'echo "Region: $(meta get parameters.region.value)"'
             - step2: 'echo "AZ: $(meta get parameters.az.value)"'
+            - step3: 'echo "Cluster: $(meta get parameters.cluster.value)"'
 ```
 
 You can also preview the parameters that are used during a build in the `Setup` -> `sd-setup-init` step.
@@ -63,6 +73,8 @@ Pipeline Preview Screenshot:
 
 ![image](../assets/parameters1-event-start.png)
 
+![image](../assets/parameters1-event-start-dropdown.png)
+
 ![image](../assets/parameters2-sd-init-step.png)
 
 ![image](../assets/parameters3-event-view.png)