Improve Jupyter Dynamic Install instructions

This commit makes a few changes:
* Uses "%mamba" over "!mamba" - has support for micromamba
* Adds "-c conda-forge" - I found this necessary, at least for
  micromamba
* Adds prefix delimiter manipulation to account for Windows paths

doc/Install.md

@@ -89,7 +89,8 @@ It is possible to dynamically install PyImageJ from within a Jupyter notebook.
 For your first cell, write:
 ```
 import sys, os
-!mamba install --yes --prefix {sys.prefix} pyimagej openjdk=11
+prefix = sys.prefix.replace("\\", "/") # Handle Windows Paths
+%mamba install --yes --prefix {prefix} -c conda-forge pyimagej openjdk=11
 os.environ['JAVA_HOME'] = os.sep.join(sys.executable.split(os.sep)[:-2] + ['jre'])
 ```