Suggest using mamba over conda (#881)

BUILD.md

@@ -45,13 +45,13 @@ Once you have this environment file, you can install the required packages by
 creating a new conda environment:
 
 ```shell
-conda env create -n legate -f <env-file>.yaml
+mamba env create -n legate -f <env-file>.yaml
 ```
 
 or by updating an existing environment:
 
 ```shell
-conda env update -f <env-file>.yaml
+mamba env update -f <env-file>.yaml
 ```
 
 ## Building through install.py

README.md

@@ -218,15 +218,15 @@ as though they are running on a single processor.
 Legate Core is available [on conda](https://anaconda.org/legate/legate-core):
 
 ```
-conda install -c nvidia -c conda-forge -c legate legate-core
+mamba install -c nvidia -c conda-forge -c legate legate-core
 ```
 
 Only linux-64 packages are available at the moment.
 
 The default package contains GPU support, and is compatible with CUDA >= 12.0
 (CUDA driver version >= r520), and Volta or later GPU architectures. There are
-also CPU-only packages available, and will be automatically selected by `conda`
-when installing on a machine without GPUs.
+also CPU-only packages available, and will be automatically selected when
+installing on a machine without GPUs.
 
 See [BUILD.md](BUILD.md) for instructions on building Legate Core from source.