add completions readme

Author: DannyBen

support/completions/README.md

@@ -0,0 +1,22 @@
+# Completions for bashly executable
+
+This directory contains support file for generating bash completions.
+
+## For developers
+
+From the root directory of the repository, run `run completions`. This will:
+
+1. Read the `completely.yaml.gtx` template
+2. Write the `completely.yaml` file
+3. Generate the `bashly-completions.bash` file
+4. Copy it to the completions directory with `sudo`
+
+## For users
+
+Install completions in one of two ways:
+
+1. Run `bashly completions --install`. This will make a best effort to copy
+   the completions script to your completions directory.
+2. If the above fails, run `bashly completions > out.bash`, then copy the file
+   manually to your completions directory (or simply get the
+   `bashly-completions.bash` from this directory).