DOC: Don't mention Mambaforge

... because it is discouraged. Use Miniforge instead.

Author: mgeier

doc/installation.ipynb

@@ -59,7 +59,7 @@
     "\n",
     "Of course you'll need Python, because both Sphinx and `nbsphinx` are implemented in Python.\n",
     "There are many ways to get Python.\n",
-    "If you don't know which one is best for you, you can try [Miniforge/Mambaforge](https://github.com/conda-forge/miniforge).\n",
+    "If you don't know which one is best for you, you can try [Miniforge](https://github.com/conda-forge/miniforge).\n",
     "\n",
     "### Sphinx\n",
     "\n",