[Rule Tuning] Tag Categorization Updates (#380)

* Add new categorization tags

* Change updated_date to 2020/10/26

Co-authored-by: Ross Wolf <31489089+rw-access@users.noreply.github.com>, @bm11100

rules/windows/execution_command_shell_started_by_powershell.toml

@@ -2,7 +2,7 @@
 creation_date = "2020/02/18"
 ecs_version = ["1.6.0"]
 maturity = "production"
-updated_date = "2020/08/03"
+updated_date = "2020/10/26"
 
 [rule]
 author = ["Elastic"]
@@ -15,7 +15,7 @@ name = "PowerShell spawning Cmd"
 risk_score = 21
 rule_id = "0f616aee-8161-4120-857e-742366f5eeb3"
 severity = "low"
-tags = ["Elastic", "Windows"]
+tags = ["Elastic", "Host", "Windows", "Threat Detection", "Execution"]
 type = "query"
 
 query = '''