Merge branch 'docs-add-index-to-operations' into 'master'

Docs: add index for `doc/administration/operations/`

See merge request gitlab-org/gitlab-ce!15852

doc/administration/index.md

@@ -35,7 +35,7 @@ Learn how to install, configure, update, and maintain your GitLab instance.
 
 - [Raketasks](../raketasks/README.md): Perform various tasks for maintenance, backups, automatic webhooks setup, etc.
   - [Backup and restore](../raketasks/backup_restore.md): Backup and restore your GitLab instance.
-- [Operations](operations.md): Keeping GitLab up and running (clean up Redis sessions, moving repositories, Sidekiq Job throttling, Sidekiq MemoryKiller, Unicorn).
+- [Operations](operations/index.md): Keeping GitLab up and running (clean up Redis sessions, moving repositories, Sidekiq Job throttling, Sidekiq MemoryKiller, Unicorn).
 - [Restart GitLab](restart_gitlab.md): Learn how to restart GitLab and its components.
 
 #### Updating GitLab

doc/administration/operations.md

-# GitLab operations
-
-- [Sidekiq MemoryKiller](operations/sidekiq_memory_killer.md)
-- [Sidekiq Job throttling](operations/sidekiq_job_throttling.md)
-- [Cleaning up Redis sessions](operations/cleaning_up_redis_sessions.md)
-- [Understanding Unicorn and unicorn-worker-killer](operations/unicorn.md)
-- [Moving repositories to a new location](operations/moving_repositories.md)
+This document was moved to [another location](operations/index.md).

doc/administration/operations/index.md

+# Performing Operations in GitLab
+
+Keep your GitLab instance up and running smoothly.
+
+- [Clean up Redis sessions](cleaning_up_redis_sessions.md): Prior to GitLab 7.3,
+user sessions did not automatically expire from Redis. If
+you have been running a large GitLab server (thousands of users) since before
+GitLab 7.3 we recommend cleaning up stale sessions to compact the Redis
+database after you upgrade to GitLab 7.3.
+- [Moving repositories](moving_repositories.md): Moving all repositories managed
+by GitLab to another file system or another server.
+- [Sidekiq job throttling](sidekiq_job_throttling.md): Throttle Sidekiq queues
+that to prioritize important jobs.
+- [Sidekiq MemoryKiller](sidekiq_memory_killer.md): Configure Sidekiq MemoryKiller
+to restart Sidekiq.
+- [Unicorn](unicorn.md): Understand Unicorn and unicorn-worker-killer.
\ No newline at end of file

doc/operations/README.md

-This document was moved to [administration/operations](../administration/operations.md).
+This document was moved to [another location](../administration/operations/index.md).