Sort docs/index.rst in alphabetical order. (#7631)

docs/index.rst

@@ -10,17 +10,17 @@
   BigQuery Storage <bigquery_storage/index>
   Bigtable <bigtable/index>
   Container <container/index>
+  Data Loss Prevention <dlp/index>
   Dataproc <dataproc/index>
   Datastore <datastore/index>
-  Data Loss Prevention <dlp/index>
   DNS <dns/index>
   Firestore <firestore/index>
   IAM <iam/index>
   IoT <iot/index>
   Key Management <kms/index>
   Language <language/index>
-  PubSub <pubsub/index>
   OSLogin <oslogin/index>
+  PubSub <pubsub/index>
   Redis <redis/index>
   Resource Manager <resource-manager/index>
   Runtime Configuration <runtimeconfig/index>
@@ -29,18 +29,18 @@
   Security Scanner <websecurityscanner/index>
   Spanner <spanner/index>
   Speech <speech/index>
+  Stackdriver Error Reporting <error-reporting/index>
+  Stackdriver Incident Response & Management <irm/index>
+  Stackdriver Logging <logging/index>
+  Stackdriver Monitoring <monitoring/index>
+  Stackdriver Trace <trace/index>
   Storage <storage/index>
   Talent <talent/index>
   Tasks <tasks/index>
   Text-to-Speech <texttospeech/index>
   Translate <translate/index>
-  Vision <vision/index>
   Video Intelligence <videointelligence/index>
-  Stackdriver Error Reporting <error-reporting/index>
-  Stackdriver Incident Response & Management <irm/index>
-  Stackdriver Logging <logging/index>
-  Stackdriver Monitoring <monitoring/index>
-  Stackdriver Trace <trace/index>
+  Vision <vision/index>
   Release History <releases>
 
 Google Cloud Client Library for Python