RunCommand: split out documentation, fixup the matcher syntax

doc/manual/src/SUMMARY.md

@@ -7,6 +7,7 @@
 - [Hydra jobs](./jobs.md)
 - [Plugins](./plugins/README.md)
   - [Declarative Projects](./plugins/declarative-projects.md)
+  - [RunCommand](./plugins/RunCommand.md)
 - [Using the external API](api.md)
 - [Webhooks](webhooks.md)
 - [Monitoring Hydra](./monitoring/README.md)

doc/manual/src/plugins/README.md

@@ -192,10 +192,12 @@ Writes InfluxDB events when a builds finished.
 - `influxdb.url`
 - `influxdb.db`
 
-## Run command
+## RunCommand
 
 Runs a shell command when the build is finished.
 
+See [The RunCommand Plugin](./RunCommand.md) for more information.
+
 ### Configuration options:
 
 - `runcommand.[].job`

doc/manual/src/plugins/RunCommand.md

@@ -0,0 +1,32 @@
+## The RunCommand Plugin
+
+Hydra supports executing a program after certain builds finish.
+This behavior is disabled by default.
+
+Hydra executes these commands under the `hydra-notify` service.
+
+### Static Commands
+
+Configure specific commands to execute after the specified matching job finishes.
+
+#### Configuration
+
+- `runcommand.[].job`
+
+A matcher for jobs to match in the format `project:jobset:job`. Defaults to `*:*:*`.
+
+**Note:** This matcher format is not a regular expression.
+The `*` is a wildcard for that entire section, partial matches are not supported.
+
+- `runcommand.[].command`
+
+Command to run. Can use the `$HYDRA_JSON` environment variable to access information about the build.
+
+### Example
+
+```xml
+<runcommand>
+  job = myProject:*:*
+  command = cat $HYDRA_JSON > /tmp/hydra-output
+</runcommand>
+```