remove some duplicate READMEs from tests

since we don't need every one included in the docs

adds detail to the one that remains

tests/venv/py2/README.rst

@@ -3,3 +3,7 @@ System - Specifying runtime environments
 
 You can specify runtime environments (such as Python 2 or 3) with a
 ``runtime.txt`` file.
+
+You can specify just the major version,
+such as `python-2` or `python-3`,
+or a minor version, such as `python-3.5`.

tests/venv/py3/README.rst

@@ -1,8 +0,0 @@
-System - Specifying runtime environments
-----------------------------------------
-
-You can specify runtime environments (such as Python 2 or 3) with a
-``runtime.txt`` file.
-
-This is an example that selects Python 3.
-If you need this level of control we recommend you use a `environment.yml`.

tests/venv/py35/README.rst

@@ -1,8 +0,0 @@
-System - Specifying runtime environments
-----------------------------------------
-
-You can specify runtime environments (such as Python 2 or 3) with a
-``runtime.txt`` file.
-
-This is an example that selects Python 3.5.
-If you need this level of control we recommend you use a `environment.yml`.