add conda-lock instructions

doc/Add-Packages-Complex-Install.md

@@ -51,7 +51,7 @@ export CPLUS_INCLUDE_PATH="$(python -c "import galsim, os; print(os.path.join(os
 python3 -m pip install --user --no-build-isolation .
 ```
 
-## Persist for Jupyter
+## NERSC Jupyter
 
 To use this new installation of BATSim in jupyter.nersc.gov, add this to `$HOME/.bashrc`:
 

doc/Installing-Your-Own-Env.md

@@ -0,0 +1,60 @@
+# Installing your own copy of desc-python
+
+Using [conda-lock](https://github.com/conda/conda-lock) you can quickly and easily install your own copy of most DESC conda environments where lock files are available.
+
+## At NERSC
+
+`conda-lock` is available for all DESC members at NERSC, just add `$CFS/lsst/utilities/bin`to your PATH
+
+`export PATH=$CFS/lsst/utilities/bin:$PATH`
+
+In this example we will install a copy of `desc-python`.
+
+git clone https://github.com/LSSTDESC/desc-python.git`
+
+To use the current production version of `desc-python`, let us assume $curBuildDir points to your desired installation directory
+
+```bash
+cp desc-python/conda/sitecustomize.py $curBuildDir
+cp desc-python/conda/desc-py-lock.yml $curBuildDir
+cp desc-python/conda/pip.config $curBuildDir
+cd $curBuildDir
+
+module unload python
+module unload cray-libsci
+module load cray-mpich-abi/8.1.30
+export CONDA_PKGS_DIRS=$curBuildDir/pkgs
+
+# use your own copy of Miniforge or you could use NERSC's python module
+url="https://github.com/conda-forge/miniforge/releases/latest/download/Miniforge3-$(uname)-$(uname -m).sh"
+curl -LO "$url"
+
+bash ./Miniforge3-Linux-x86_64.sh -b -p $curBuildDir/py
+source $curBuildDir/py/etc/profile.d/conda.sh
+conda activate base
+
+export PIP_CONFIG_FILE=$curBuildDir/pip.config
+
+conda-lock install --mamba -n my-desc-python $curBuildDir/desc-py-lock.yml
+
+conda activate my-desc-python
+
+conda env config vars set CSL_DIR=${CONDA_PREFIX}/cosmosis-standard-library
+cd ${CONDA_PREFIX}
+source ${CONDA_PREFIX}/bin/cosmosis-configure
+cosmosis-build-standard-library main
+```
+
+And that's it!
+
+#### To use your my-desc-python environment
+
+```bash
+module unload python
+module unload cray-libsci
+module load cray-mpich-abi/8.1.30
+source $curBuildDir/bin/activate
+conda activate my-desc-python
+```
+
+