Adds development docs

Signed-off-by: PuneetPunamiya <ppunamiy@redhat.com>

docs/DEVELOPEMENT.md

@@ -0,0 +1,66 @@
+# Installing Manual Approval Gate
+
+NOTE:- You need to install [tektoncd/pipeline](https://github.com/tektoncd/pipeline/blob/main/docs/install.md)
+
+1. Manual Approval Gate Installation
+   *  On Kubernetes
+       ```
+       make apply
+       ```
+   * On Openshift
+      ```
+      make TARGET=openshift apply
+      ```
+
+2. Install a pipelineRun which has approval task as one of the task in the pipelin
+   - For example 
+     ```yaml
+     apiVersion: tekton.dev/v1beta1
+     kind: PipelineRun
+     metadata:
+       generateName: pr-custom-task-beta-
+     spec:
+       pipelineSpec:
+         tasks:
+           - name: before    
+             taskSpec:
+               steps:
+                 - image: busybox
+                   name: before
+                   script: echo before wait
+           - name: wait                     👈 Wait task with kind as `ApprovalTask`                           
+             taskRef:
+               apiVersion: openshift-pipelines.org/v1alpha1
+               kind: ApprovalTask
+             runAfter: ['before']
+           - name: after
+             taskSpec:
+               steps:
+                 - image: busybox
+                   name: after
+                   script: echo after wait
+             runAfter: ['wait']
+    
+     ```
+   Install the above pipelineRun
+    
+    ```shell
+    kubectl create -f <pipeline.yaml>
+    ```
+   
+    **NOTE** :- _Once the pipelineRun is started after the execution of first task is done, it will create a customRun for that approval task and the pipeline will be in wait state till it gets the approval from the user. The name of the approvalTask is the same of customRun which is created. 
+As of today only `"true"` and `"false"` are supported. If user passes the approval as `"true"` then pipeline will proceed to execute the further tasks and if `"false"` is provided then in that case it will fail the pipeline_
+
+
+3. Now start the api server
+    ```shell
+    go run ./cmd/approver/main.go
+    ```
+4. Now approve/reject the approval task using curl request
+
+    ```shell
+    curl --header "Content-Type: application/json" \                                                                                           
+    --request POST \
+    --data '{"approved":"false", "namespace":"default"}' \
+    http://localhost:8000/approvaltask/<approvalTaskName>
+    ```