Add TeamCity instructions (apache#5379)

ci/README_TeamCity.md

@@ -0,0 +1,15 @@
+## Becoming a project administrator
+Druid committers shall obtain a status of a [Druid project](
+https://teamcity.jetbrains.com/project.html?projectId=OpenSourceProjects_Druid)
+administrator. First, the Druid committer needs to log in teamcity.jetbrains.com using his Github account.
+Then, somebody who is already a project administrator needs to do the following:
+
+ 1. Follow the "Administration" link in the top-right corner of the page
+ 2. Follow the "Users" link in the "User Management" section in the menu on the left
+ 3. Type the comitter's Github handle in the "Find users" text input, press "Filter"
+ 4. Select the comitter
+ 5. Press the "Assign roles" button in the bottom of the page
+ 6. Select "Role: Project administrator" and "Scope: Open-source project -> Druid" in the inputs, press "Assign"
+
+## Restarting a build
+A project administrator could restart a build by pressing the "Run" button on the build page.