Declare our new dependencies

src/allmydata/_auto_deps.py

@@ -104,6 +104,9 @@ install_requires = [
     # won't end up stuck on Eliot 1.6.100 with a critical fix only present in
     # 1.6.101.  And if we do, I know how to deal with that situation.
     "eliot >= 1.6.0, <= 1.6.100",
+
+    # A great way to define types of values.
+    "attrs >= 18.2.0",
 ]
 
 # Includes some indirect dependencies, but does not include allmydata.
@@ -133,6 +136,7 @@ package_imports = [
     ('magic-wormhole',   'wormhole'),
     ('setuptools',       'setuptools'),
     ('eliot',            'eliot'),
+    ('attrs',            'attr'),
 ]
 
 # Dependencies for which we don't know how to get a version number at run-time.