DOC: update conda-forge installation instruction

Author: dragonyanglong

CHANGELOG.md

@@ -18,5 +18,6 @@ Notable differences from version 1.2.
 
 ### Fixed
 
--  Patch variable to avoid naming problems and Xcode collision on MacOS & Linux.
--  Fix g++ w/ambiguous isnan on Linux.
+- Patch variable to avoid naming problems and Xcode collision on MacOS & Linux.
+- Fix g++ w/ambiguous isnan on Linux.
+- Fix the PY_SSIZE_T_CLEAN macro for py3.10.

README.rst

@@ -59,10 +59,9 @@ INSTALLATION
 ------------------------------------------------------------------------
 
 The preferred method is to use Anaconda Python and install from the
-"diffpy" channel of Anaconda packages ::
+"conda-forge" channel of Anaconda packages ::
 
-   conda config --add channels diffpy
-   conda install diffpy.pdffit2
+   conda install -c conda-forge diffpy.pdffit2
 
 If you don't use Anaconda or prefer to install from sources, make
 sure the required software is in place and run ::