This patch splits send-to-channel-slack task from the slackmessage directroy

Changes include:
  - moves send-to-channel-slack task to the task directory
  - copies and modifies readme from slackmessage to send-to-channel-slack
  - copies owners file from slackmessage

Issue: #386

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

task/send-to-channel-slack/0.1/OWNERS

@@ -0,0 +1,7 @@
+approvers:
+- akihikokuroda
+- ncskier
+reviewers:
+- akihikokuroda
+- ncskier
+

task/send-to-channel-slack/0.1/README.md

@@ -0,0 +1,65 @@
+# Post a message to slack
+
+These tasks post a simple message to a slack channel.  There are multiple ways to send
+a message to slack. Each task here uses different method.
+
+
+# send-to-channel-slack
+
+This task uses chat.postMessage slack REST api to send the message.
+Follow instructions [here](https://api.slack.com/messaging/sending) to obtain the OAuth access token for the bot app with `chat:write` scope.
+The app must join the channel before the message posted by this task run. (invite the app in the channel)
+
+## Install the Task and create a secret
+
+```
+kubectl apply -f https://raw.githubusercontent.com/tektoncd/catalog/master/task/send-to-channel-slack/0.1/send-to-channel-slack.yaml
+```
+
+Create a secret that has the OAuth token of the bot app.
+
+Example token-secret.yaml
+```
+kind: Secret
+apiVersion: v1
+metadata:
+  name: token-secret
+stringData:
+  token: {OAuth token for the bot app}
+```
+
+Example kubectl command
+```
+kubectl apply -f token-secret.yaml
+```
+
+## Inputs
+
+### Parameters
+
+* **token-secret**: The name of the secret that has the OAuth token.  The key for the OAuth-token is token
+
+* **channel**: [channel id](https://api.slack.com/messaging/retrieving#finding_conversation) or channel name where the message is posted
+
+* **message**: Plain text message to be posted in the slack channel
+
+## Usage
+
+This TaskRun runs the Task to post a message to the channel.
+
+```
+apiVersion: tekton.dev/v1beta1
+kind: TaskRun
+metadata:
+  name: run-send-to-channel-slack
+spec:
+  params:
+  - name: token-secret
+    value: token-secret
+  - name: channel
+    value: {CHANNEL ID}
+  - name: message
+    value: "Hello from Tekton!"
+  taskRef:
+    name: send-to-channel-slack
+```