DOC Note down matplotlib dependency in README.rst (scikit-learn#14322)

Author: qinhanmin2014

README.rst

@@ -52,11 +52,13 @@ scikit-learn requires:
 - SciPy (>= 0.17.0)
 - joblib (>= 0.11)
 
-**Scikit-learn 0.20 was the last version to support Python 2.7.**
+**Scikit-learn 0.20 was the last version to support Python 2.7 and Python 3.4.**
 scikit-learn 0.21 and later require Python 3.5 or newer.
 
-For running the examples Matplotlib >= 1.5.1 is required. A few examples
-require scikit-image >= 0.12.3, a few examples require pandas >= 0.18.0.
+Scikit-learn plotting capabilities (i.e., functions start with "plot_") require
+Matplotlib (>= 1.5.1). For running the examples Matplotlib >= 1.5.1 is
+required. A few examples require scikit-image >= 0.12.3, a few examples require
+pandas >= 0.18.0.
 
 scikit-learn also uses CBLAS, the C interface to the Basic Linear Algebra
 Subprograms library. scikit-learn comes with a reference implementation, but

doc/install.rst

@@ -23,8 +23,9 @@ Scikit-learn requires:
 - joblib (>= 0.11)
 
 Scikit-learn plotting capabilities (i.e., functions start with "plot_") require
-Matplotlib (>= 1.5.1). Some of the scikit-learn examples might require one or
-more extra dependencies: scikit-image (>= 0.12.3), pandas (>= 0.18.0).
+Matplotlib (>= 1.5.1). For running the examples Matplotlib >= 1.5.1 is
+required. A few examples require scikit-image >= 0.12.3, a few examples require
+pandas >= 0.18.0.
 
 .. warning::