Add FWd logging docs (#53)

DEVELOPING.md

@@ -35,3 +35,43 @@ npm install (path to `filewatcherd-(version).tar.gz` from step A)
 
 Restart VS Code. Then, hit F5 to launch the debugger. It should build, compile, and start the Codewind VS Code extension. See [DEVELOPING.md](https://github.com/eclipse/codewind-vscode/blob/master/DEVELOPING.md) for additional information on launching a VS Code extension.
 
+
+# How to view the Codewind Filewatchers logs
+
+The filewatcher daemons automatically log filewatcher-specific log statements to a codewind-specific directory on the file system. At most the last 24MB of log files will be retained (rolling logs), and any existing log files are deleted on IDE startup.
+
+
+### Locations of filewatcher log file(s), on the file system:
+
+- When running in Codewind Eclipse: `(eclipse workspace)/.metadata`
+- When running in Codewind VSCode:
+  - In VSCode, `Help` > `Toggle Developer Tools` > `Console`
+  - Then in the Filter box, enter `Logger initialized at`. For example: `Logger.js.setLogFilePath():62]: Logger initialized at c:\Users\JONATHANWest\AppData\Roaming\Code\logs\20190624T145813\exthost3\IBM.codewind\codewind.log`
+  - Open the directory containing `codewind.log`, and look for `filewatcherd-(...).log`
+- When running standalone: `(user home dir)/.codewind`
+
+
+### Log filename, in above directory:  
+- `filewatcherd-(#).log` (there should exist at least one, and at most two, log files; the log file with the larger `#` is the most recent.
+
+
+### How to switch a filewatcher to the more verbose 'DEBUG' log level
+
+Filewatchers default to an `INFO` log level. If you wish to see (or are asked to enable) the more verbose `DEBUG` log level, do as follows.
+
+#### Steps:
+1. Close VSCode and/or Eclipse, to ensure the existing filewatcher is stopped.
+2. Set the following [system environment variable](https://superuser.com/questions/284342/what-are-path-and-other-environment-variables-and-how-can-i-set-or-use-them):
+- `filewatcher_log_level` to `debug`
+3. Open a new Command Prompt or Terminal and type:
+- Windows: `echo %filewatcher_log_level%`
+- Linux/MacOS: `echo $filewatcher_log_level`
+- In both cases, you should see `debug`. If you do not, your system environment variable is not set correctly.
+4. Start VSCode or Eclispe.
+
+To verify the change has taken effect, open the `filewatcherd-(...).log` file and look for a line like this:
+```
+codewind-filewatcher logging to C:\Users\your-username\.codewind with log level DEBUG
+```
+
+