Update docs with developer defaults

docs/internals.md

@@ -8,6 +8,7 @@ The resulting Docker image contains the following:
 * MQ installation (under `/opt/mqm`)
 * Three additional programs, to enable running in a containerized environment:
    - `runmqserver` - The main process, which creates and runs a queue manager
+   - `runmqdevserver` - The main process for MQ Advanced for Developers
    - `chkmqhealthy` - Checks the health of the queue manager.  This can be used by (say) a Kubernetes liveness probe.
    - `chkmqready` - Checks if the queue manager is ready for work.  This can be used by (say) a Kubernetes readiness probe.
 
@@ -23,3 +24,15 @@ The `runmqserver` command has the following responsibilities:
     - Works as PID 1, so is responsible for [reaping zombie processes](https://blog.phusion.nl/2015/01/20/docker-and-the-pid-1-zombie-reaping-problem/)
 * Creating and starting a queue manager
 * Configuring the queue manager, by running any MQSC scripts found under `/etc/mqm`
+* Indicates to the `chkmqready` command that configuration is complete, and that normal readiness checking can happen.  This is done by writing a file into `/run/runmqserver`
+
+In addition, for MQ Advanced for Developers only, the web server is started.
+
+## runmqdevserver
+The `runmqdevserver` command is added to the MQ Advanced for Developers image only.  It does the following, before invoking `runmqserver`:
+
+1. Sets passwords based on supplied environment variables
+2. Generates MQSC files to put in `/etc/mqm`, based on a template, which is updated with values based on supplied environment variables.
+3. If requested, it creates TLS key stores under `/run/runmqdevserver`, and configures MQ and the web server to use them
+
+A special version of `runmqserver` is used in the developer image, which performs extra actions like starting the web server.  This is built using the `mqdev` [build constraint](https://golang.org/pkg/go/build/#hdr-Build_Constraints).