Add example for builder podspec (#1374)

examples/spec-example/podspec-example/README.md

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+# Adding podspec for builder of environment
+
+If you see the files in the `specs` directory you will get to know that we have just generated the 
+environment spec using the command 
+```
+fission env create --name python --image fission/python-env --builder fission/python-builder --spec
+```
+and changed the env-python.yaml file to have below `podspec` for builder for the environment.
+
+```
+nodeSelector:
+  machinecap: high
+tolerations:
+- key: "env"
+  value: "prod"
+  operator: "Equal"
+  effect: "NoSchedule"
+
+```
+
+If we create this environment, the builder pod that will be created will have the `PodSpec` that 
+we have mentioned for builder in the environment spec.
+
+

examples/spec-example/podspec-example/specs/README

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+
+Fission Specs
+=============
+
+This is a set of specifications for a Fission app.  This includes functions,
+environments, and triggers; we collectively call these things "resources".
+
+How to use these specs
+----------------------
+
+These specs are handled with the 'fission spec' command.  See 'fission spec --help'.
+
+'fission spec apply' will "apply" all resources specified in this directory to your
+cluster.  That means it checks what resources exist on your cluster, what resources are
+specified in the specs directory, and reconciles the difference by creating, updating or
+deleting resources on the cluster.
+
+'fission spec apply' will also package up your source code (or compiled binaries) and
+upload the archives to the cluster if needed.  It uses 'ArchiveUploadSpec' resources in
+this directory to figure out which files to archive.
+
+You can use 'fission spec apply --watch' to watch for file changes and continuously keep
+the cluster updated.
+
+You can add YAMLs to this directory by writing them manually, but it's easier to generate
+them.  Use 'fission function create --spec' to generate a function spec,
+'fission environment create --spec' to generate an environment spec, and so on.
+
+You can edit any of the files in this directory, except 'fission-deployment-config.yaml',
+which contains a UID that you should never change.  To apply your changes simply use
+'fission spec apply'.
+
+fission-deployment-config.yaml
+------------------------------
+
+fission-deployment-config.yaml contains a UID.  This UID is what fission uses to correlate
+resources on the cluster to resources in this directory.
+
+All resources created by 'fission spec apply' are annotated with this UID.  Resources on
+the cluster that are _not_ annotated with this UID are never modified or deleted by
+fission.
+

examples/spec-example/podspec-example/specs/env-python.yaml

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+apiVersion: fission.io/v1
+kind: Environment
+metadata:
+  creationTimestamp: null
+  name: python
+  namespace: default
+spec:
+  builder:
+    command: build
+    image: fission/python-builder
+    podspec:
+      nodeSelector:
+        machinecap: high
+      tolerations:
+      - key: "env"
+        value: "prod"
+        operator: "Equal"
+        effect: "NoSchedule"
+  keeparchive: false
+  poolsize: 3
+  resources: {}
+  runtime:
+    image: fission/python-env
+  terminationGracePeriod: 360
+  version: 2

examples/spec-example/podspec-example/specs/fission-deployment-config.yaml

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+# This file is generated by the 'fission spec init' command.
+# See the README in this directory for background and usage information.
+# Do not edit the UID below: that will break 'fission spec apply'
+apiVersion: fission.io/v1
+kind: DeploymentConfig
+name: podspec-example
+uid: c0803d62-03a2-4934-b9b2-82f2a221a333