DOC: update installation steps.

Author: dragonyanglong

README.rst

@@ -57,14 +57,15 @@ INSTALLATION
 ------------------------------------------------------------------------
 
 The preferred method is to use Anaconda Python and install from the
-"conda-forge" channel of Anaconda packages. The `conda-forge` channel can be achieved by adding `conda-forge` to your channels with ::
+"conda-forge" channel of Anaconda packages. The `conda-forge` channel
+can be achieved by adding `conda-forge` to your channels with ::
 
-conda config --add channels conda-forge
-conda config --set channel_priority strict
+   conda config --add channels conda-forge
+   conda config --set channel_priority strict
 
 Once the `conda-forge` channel has been enabled, `diffpy.pdffit2` can be installed with `conda` ::
 
-conda install diffpy.pdffit2
+   conda install diffpy.pdffit2
 
 PDFgui can be then started from a terminal ("Anaconda Prompt" on
 Windows) by executing the "pdfgui" program.  An alternative