requirements.txt: Classify and provide a rationale for each dependency

requirements.txt

@@ -1,9 +1,17 @@
+# mandatory:
+
 setuptools
-chardet
-pytz;python_version<'3.9'
-python-dateutil
-python-gnupg
-feedparser
-PySocks
-cryptography
-pyxmpp2-scram
+
+# optional core dependencies:
+
+chardet                     # to detect encoding of incoming IRC lines, if they are not in UTF-8
+python-gnupg                # for authenticated based on GPG tokens
+PySocks                     # for SOCKS proxy (typically used to connect to IRC via Tor)
+pyxmpp2-scram               # for the scram-sha-256 SASL mechanism
+
+# optional plugin dependencies:
+
+cryptography                # required to load the Fediverse plugin (used to implement HTTP signatures to support Mastodon instances with AUTHORIZED_FETCH=true)
+feedparser                  # required to load the RSS plugin
+pytz;python_version<'3.9'   # enables timezone manipulation in the Time and Geography plugins. On Python >=3.9, the standard library is used instead
+python-dateutil             # enable fancy time string parsing in the Time plugin