[QA][Code Coverage] Team Assignment Docs Update (#78890)

[QA][Code Coverage] Team Assignment Docs Update (#78890)

Author: wayneseymour

src/dev/code_coverage/docs/team_assignment/README.md

@@ -1,8 +1,41 @@
-# Team Assignment Ingestion Pipeline
+# Code Coverage Team Assignments
 
-Team assignment will occur once per ci run.
-Team assignment uses an ingest pipeline.
+Team assignment occurs once per ci run.
 
-The coverage user has the coverage admin role.
+The "orchestration" entry point is a [Jenkinsfile Scripted Pipeline](https://github.com/elastic/kibana/blob/f73bc48b3bbbb5ad2042c1aa267aea2150b7b742/.ci/Jenkinsfile_coverage#L21)  
+This Jenkinsfile runs a [shell script](https://github.com/elastic/kibana/blob/master/src/dev/code_coverage/shell_scripts/generate_team_assignments_and_ingest_coverage.sh#L33) that kicks everything off.  
+The end result is the data is ingested to our [Kibana Stats Cluster](https://kibana-stats.elastic.dev/app/dashboards#/view/58b8db70-62f9-11ea-8312-7f2d69b79843?_g=(filters%3A!()%2CrefreshInterval%3A(pause%3A!t%2Cvalue%3A0)%2Ctime%3A(from%3Anow-7d%2Cto%3Anow)))
 
-This role must have the rights depicted below ![Cluster Rights](./security_privleges.png)
+## Team Assignment Parsing (from .github/CODEOWNERS)  
+We add additional metadata to the CODEOWNERS file.  
+This metadata allows users to assign teams to paths, in a friendly location.  
+Example CODEOWNERS Block:  
+_notice the coverage delimiter `#CC# ...`_
+```
+/x-pack/test/functional/es_archives/endpoint/ @elastic/endpoint-app-team @elastic/siem
+/x-pack/test/plugin_functional/plugins/resolver_test/ @elastic/endpoint-app-team @elastic/siem
+/x-pack/test/plugin_functional/test_suites/resolver/ @elastic/endpoint-app-team @elastic/siem
+#CC# /x-pack/legacy/plugins/siem/ @elastic/siem
+#CC# /x-pack/plugins/siem/ @elastic/siem
+#CC# /x-pack/plugins/security_solution/ @elastic/siem
+```
+The first 3 lines above fill the usual purpose of the CODEOWNERS file and cause PRs modifying files in these paths to require approval by the listed team(s).  
+They also attribute files in those paths for purpose of code coverage reporting.  
+The last 3 lines above ONLY attribute files in those paths for purpose of code coverage reporting.  
+
+## Team Assignment Data File Creation (Before Ingestion)
+We create a data file containing all paths in the repo, with a team assigned.   
+Example Team Assignments Block: 
+```
+x-pack/plugins/security_solution/common/constants.ts siem
+x-pack/plugins/security_solution/common/detection_engine/build_exceptions_query.test.ts siem
+x-pack/plugins/security_solution/common/detection_engine/build_exceptions_query.ts siem
+...
+```
+
+## Team Assignment Data File Usage (During Code Coverage Ingestion) 
+Subsequently, we use the data file during ingestion.
+We search the data file, for any given "coveredFilePath"
+ - Given the above assignments block, and lets say the "coveredFilePath" during ingestion is 
+   - `x-pack/plugins/security_solution/common/constants.ts`
+   - The team assignment would be `siem` in our [Kibana Stats Cluster](https://kibana-stats.elastic.dev/app/dashboards#/view/58b8db70-62f9-11ea-8312-7f2d69b79843?_g=(filters%3A!()%2CrefreshInterval%3A(pause%3A!t%2Cvalue%3A0)%2Ctime%3A(from%3Anow-7d%2Cto%3Anow)))