Change -e to -r in pip install -r requirements/test.in

docs/why.rst

@@ -103,7 +103,7 @@ Now installation command is
 
 .. code-block:: shell
 
-    pip install -e requirements/test.in
+    pip install -r requirements/test.in
 
 For one single time (exceptionally to show how unacceptable is this task)
 let's manually compose ``requirements/test.txt``.
@@ -245,4 +245,4 @@ Some of the benefits are achievable with other methods, but I want to be general
    not whenever they are released.
 5. Different environments are separated into different files.
 6. ``*.in`` files are small and manageable because they store only direct dependencies.
-7. ``*.txt`` files are exhaustive and precise (but you don't need to edit them).
+7. ``*.txt`` files are exhaustive and precise (but you don't need to edit them).