warn against sorting requirements

Co-authored-by: Joshua Harlow <harlowja@gmail.com>
Addresses-Bug: #1365061

Change-Id: I64ae9191863564e278a35d42ec9cd743a233028e

optional-requirements.txt

@@ -1,8 +1,11 @@
-# This file lists dependencies that are used by different
-# pluggable (optional) parts of TaskFlow, like engines
-# or persistence backends. They are not strictly required
-# by TaskFlow (you can use TaskFlow without them), but
-# so they don't go to requirements.txt.
+# This file lists dependencies that are used by different pluggable (optional)
+# parts of TaskFlow, like engines or persistence backends. They are not
+# strictly required by TaskFlow (aka you can use TaskFlow without them), so
+# they don't go into one of the requirements.txt files.
+
+# The order of packages is significant, because pip processes them in the order
+# of appearance. Changing the order has an impact on the overall integration
+# process, which may cause wedges in the gate later.
 
 # Database (sqlalchemy) persistence:
 SQLAlchemy>=0.7.8,<=0.9.99

requirements-py2.txt

@@ -1,3 +1,7 @@
+# The order of packages is significant, because pip processes them in the order
+# of appearance. Changing the order has an impact on the overall integration
+# process, which may cause wedges in the gate later.
+
 # Packages needed for using this library.
 anyjson>=0.3.3
 iso8601>=0.1.9

requirements-py3.txt

@@ -1,3 +1,7 @@
+# The order of packages is significant, because pip processes them in the order
+# of appearance. Changing the order has an impact on the overall integration
+# process, which may cause wedges in the gate later.
+
 # Packages needed for using this library.
 anyjson>=0.3.3
 iso8601>=0.1.9

test-requirements.txt

@@ -1,3 +1,7 @@
+# The order of packages is significant, because pip processes them in the order
+# of appearance. Changing the order has an impact on the overall integration
+# process, which may cause wedges in the gate later.
+
 hacking>=0.9.2,<0.10
 discover
 coverage>=3.6