Update installation instructions

Author: SylvainCorlay

README.md

@@ -50,10 +50,10 @@ s
 
 ### Installation of the standalone C++ library
 
-`xtensor-r` a header-only C++ library. It has been packaged for the conda package manager.
+`xtensor-r` a header-only C++ library. It has been packaged for the mamba (or conda) package manager.
 
 ```bash
-conda install xtensor-r -c conda-forge
+mamba install xtensor-r -c conda-forge
 ```
 
 `xtensor-r` can be installed from source with cmake in any installation prefix. For example, on unix systems

docs/source/installation.rst

@@ -27,14 +27,14 @@ Besides the xtendor-r headers, all these methods place the `cmake` project confi
 
 .. image:: conda.svg
 
-Using the conda package
------------------------
+Using the conda-forge package
+-----------------------------
 
-A package for xtensor-r is available on the conda package manager.
+A package for xtensor-r is available on the mamba (or conda) package manager.
 
 .. code::
 
-    conda install -c conda-forge xtensor-r
+    mamba install -c conda-forge xtensor-r
 
 .. image:: cmake.svg