add docs for idle runners

Author: aktech

docs/reference/idle_runners.md

@@ -0,0 +1,93 @@
+---
+id: idle-runners
+description: Keep some runners idle to avoid latency
+image: "https://cirun.io/cirun-summary-image-v4.png"
+keywords: [Cirun, idle-runners, Runners]
+---
+
+# Idle Runners
+
+Cirun creates runners on-demand on various cloud providers, which takes sometimes a
+couple of minutes or more. This might not be suitable for use cases where you need
+to run CI jobs almost instantly like GitHub hosted runners. This is why we introduced
+the ability to keep "x" number of runners always (or at some specified times) running.
+This will help you run workflows almost instantly.
+
+:::info
+Idle runners does not mean that the same machine will be re-used for jobs.
+Runners are destroyed after the job completes. Idle runner configuration
+makes sure that given number of runners are always available, as in a runner
+is created if one of the runners picks up a job.
+:::
+
+## Examples
+
+### Make 4 runners always available from 9 AM - 5 PM on Monday to Friday and 1 on weekend:
+
+```yaml
+runners:
+  - name: aws-cpu-runner
+    cloud: aws
+    instance_type: t2.medium
+    machine_image: ami-06fd8a495a537da8b
+    preemptible: true
+    labels:
+      - cirun-runner
+    idle:
+      schedule:
+        - day: mon-fri
+          time: 5-7
+          timezone: UTC
+          replicas: 4
+        - day: sat-sun
+          time: 8-17
+          timezone: UTC
+          replicas: 1
+```
+
+
+### Make 4 runners always available from 9 AM - 5 PM on Monday to Friday and none on weekend:
+
+```yaml
+runners:
+  - name: aws-cpu-runner
+    cloud: aws
+    instance_type: t2.medium
+    machine_image: ami-06fd8a495a537da8b
+    preemptible: true
+    labels:
+      - cirun-runner
+    idle:
+      schedule:
+        - day: mon-fri
+          time: 5-7
+          timezone: UTC
+          replicas: 4
+```
+
+### Make variable number of runners available on different days of week:
+
+```yaml
+runners:
+  - name: aws-cpu-runner
+    cloud: aws
+    instance_type: t2.medium
+    machine_image: ami-06fd8a495a537da8b
+    preemptible: true
+    labels:
+      - cirun-runner
+    idle:
+      schedule:
+        - day: mon
+          time: 5-7
+          timezone: UTC
+          replicas: 2
+        - day: wed
+          time: 5-7
+          timezone: UTC
+          replicas: 3
+        - day: fri
+          time: 5-7
+          timezone: UTC
+          replicas: 4
+```

sidebars.js

@@ -39,6 +39,7 @@ module.exports = {
         "reference/developer-api",
         "reference/organization-runner-configuration",
         "reference/access-control",
+        "reference/idle-runners",
       ],
     },
     {