pipeline: filters: added link from summary page

Added link from summary.md (overwritten by conflit).

Signed-off-by: Oleg Mukhin <[email protected]>

Author: olegmukhin

SUMMARY.md

@@ -150,6 +150,7 @@
   * [Grep](pipeline/filters/grep.md)
   * [Kubernetes](pipeline/filters/kubernetes.md)
   * [Logs to metrics](pipeline/filters/log_to_metrics.md)
+  * [Lookup](pipeline/filters/lookup.md)
   * [Lua](pipeline/filters/lua.md)
   * [Modify](pipeline/filters/modify.md)
   * [Multiline](pipeline/filters/multiline-stacktrace.md)