Add ParentPrefixSelector guide empty docs

ParentPrefixSelectorGuide.md

@@ -0,0 +1,51 @@
+# A guide of `ParentPrefixSelector` in `PrefixClaim`
+
+There are 2 ways to make a Prefix claim:
+- provide a `parentPrefix`
+- provide a `parentPrefixSelector`
+
+In this documentation, we will focus on the `parentPrefixSelector` only.
+
+# CRD format
+
+The following is a sample of utilizing the `parentPrefixSelector`:
+```bash
+apiVersion: netbox.dev/v1
+kind: PrefixClaim
+metadata:
+  labels:
+    app.kubernetes.io/name: netbox-operator
+    app.kubernetes.io/managed-by: kustomize
+  name: prefixclaim-customfields-sample
+spec:
+  tenant: "MY_TENANT"
+  site: "DM-Akron"
+  description: "some description"
+  comments: "your comments"
+  preserveInNetbox: true
+  prefixLength: "/31"
+  parentPrefixSelector: 
+    tenant: "MY_TENANT_2"
+    site: "DM-Bryon"
+    environment: "Production"
+    poolName: "Pool 1"
+```
+
+## `Spec.tenant` and `Spec.site`
+
+Please provide the *name*, not the *slug* value
+
+## `parentPrefixSelector`
+
+The `parentPrefixSelector` is a key-value map, where all the entries are of data type `<string-string>`.
+
+The `parentPrefixSelector` is a set of query conditions for selecting a set of prefixes that can be used as the parent prefix.
+
+The fields that can be used as query conditions in the `parentPrefixSelector` are:
+- `tenant` and `site`
+    - these 2 fields come by design with NetBox, so you do *not* need to create custom fields for them
+    - please provide the *name*, not the *slug* value
+    - if either of the value is missing, it will *not* inherit from the tenant and site from the Spec
+- custom fields
+    - the data types tested and supported so far are `string`, `integer`, and `boolean`
+    - for `boolean` type, please use `true` and `false` as the value

README.md

@@ -58,6 +58,13 @@ Use Cases for this Restoration:
 - Disaster Recovery: In case the cluster is lost, IP Addresses can be restored with the IPAddressClaim only
 - Sticky IPs: Some services do not handle changes to IPs well. This ensures the IP/Prefix assigned to a Custom Resource is always the same.
 
+# `ParentPrefixSelector` in `PrefixClaim`
+
+Please read [ParentPrefixSelector guide] for more information!
+
+[ParentPrefixSelector guide]: ./ParentPrefixSelectorGuide.md
+
+
 # Project Distribution
 
 Following are the steps to build the installer and distribute this project to users.