AppnexusAst bidadapter markdown file (prebid#1696)

* added appnexusAst bidadapter markdown file

* updated mediatype native config

Author: jaiminpanchal27

modules/appnexusAstBidAdapter.md

@@ -0,0 +1,103 @@
+# Overview
+
+```
+Module Name:  AppnexusAst Bid Adapter
+Module Type:  Bidder Adapter
+Maintainer: info@prebid.org
+```
+
+# Description
+
+Connects to Appnexus exchange for bids.
+
+AppnexusAst bid adapter supports Banner, Video (instream and outstream) and Native.
+
+# Test Parameters
+```
+var adUnits = [
+   // Banner adUnit
+   {
+       code: 'banner-div',
+       sizes: [[300, 250], [300,600]],
+       bids: [{
+         bidder: 'appnexusAst',
+         params: {
+           placementId: '10433394'
+         }
+       }]
+   },
+   // Native adUnit
+   {
+      code: 'native-div',
+      sizes: [[300, 250], [300,600]],
+      mediaTypes: {
+        native: {
+          title: {
+            required: true,
+            len: 80
+          },
+          body: {
+            required: true
+          },
+          brand: {
+            required: true
+          },
+          image: {
+            required: true
+          },
+          clickUrl: {
+            required: true
+          },
+        }
+      },
+      bids: [{
+        bidder: 'appnexusAst',
+        params: {
+          placementId: '9880618'
+        }
+      }]
+   },
+   // Video instream adUnit
+   {
+      code: 'video-instream',
+      sizes: [640, 480],
+      mediaTypes: {
+        video: {
+          context: 'instream'
+        },
+      },
+      bids: [{
+        bidder: 'appnexusAst',
+        params: {
+          placementId: '9333431',
+          video: {
+            skippable: true,
+            playback_methods: ['auto_play_sound_off']
+          }
+        }
+      }]
+   },
+   // Video outstream adUnit
+   {
+     code: 'video-outstream',
+     sizes: [[640, 480]],
+     mediaTypes: {
+       video: {
+         context: 'outstream'
+       }
+     },
+     bids: [
+       {
+         bidder: 'appnexusAst',
+         params: {
+           placementId: '5768085',
+           video: {
+             skippable: true,
+             playback_method: ['auto_play_sound_off']
+           }
+         }
+       }
+     ]
+   }
+];
+```