Update glossary.md

Author: ksuess

docs/glossary.md

@@ -67,6 +67,12 @@ pip
     pip is the package installer for Python.
     See [tool recommendations](https://packaging.python.org/en/latest/guides/tool-recommendations/) for more information.
 
+pm2
+    [PM2](https://pm2.keymetrics.io/) is a daemon process manager.
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+REST API
+    TODO REST API in general. TODO REST API of Plone.
+
 S3
     [Amazon Web Services S3](https://aws.amazon.com/s3/).
     Object storage built to store and retrieve any amount of data from anywhere.
@@ -77,6 +83,14 @@ TTW
 
 
 
+% TODO sort subsequent glossary terms alphabetically
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 Amazon Opsworks
     [AWS OpsWorks](https://aws.amazon.com/opsworks/) is a configuration management service that uses Chef, an automation platform that treats server configurations as code.