add zipapp info

Added installation instructions for PyPi and ZipApp.

Author: m-bartlett

README.md

@@ -41,10 +41,31 @@ is only stored on disk one time. If snapshots are deleted and a given hashed con
 then the `--gargbage-collect` flag will prompt `cacheback` to purge these unused hash-named files to recover storage space.
 
 ## Install
+
+## PyPi
 ```
 pip install cacheback-snapshot
 ```
 
+## ZipApp
+Create an executable single-file using python's zipapp feature by running `./scripts/install-zipapp.sh <install_dir>`, for example:
+
+```console
+$ ./scripts/install-zipapp.sh ~/.local/bin/
+Processing ./.
+  Installing build dependencies ... done
+  Getting requirements to build wheel ... done
+  Preparing metadata (pyproject.toml) ... done
+Building wheels for collected packages: cacheback-snapshot
+  Building wheel for cacheback-snapshot (pyproject.toml) ... done
+Successfully built cacheback-snapshot
+Installing collected packages: cacheback-snapshot
+Successfully installed cacheback-snapshot
+
+$ ~/.local/bin/cacheback --help
+usage: python /home/m/.local/bin/cacheback ...
+```
+
 ## Usage
 >[!NOTE]
 > The first time taking a snapshot will take much longer than subsequent snapshots, since the first run will need to copy any and all files to the snapshot storage directory. The real magic of this tool happens on the *subsequent* snapshots that target mostly the same directories.