Document CLI use

docs/cli_use.md

@@ -1,3 +1,55 @@
 # Using the Transdoc CLI
 
-Transdoc can be accessed using
+Transdoc can be accessed using a CLI with the `transdoc` command.
+
+```bash
+$ transdoc --version
+transdoc, version 1.0.0
+```
+
+## Rule file
+
+You can specify a Python file containing the Transdoc rules you wish to use
+while transforming your documentation using the `-r` flag.
+
+```bash
+$ transdoc -r path/to/rules.py
+...
+```
+
+## Input files
+
+You can specify an input file or directory as the primary argument.
+
+```bash
+$ transdoc input.txt
+...
+```
+
+If a file is given, its transformed output will be written to `stdout`.
+Otherwise, you must specify an output directory, or use the `--dryrun` flag.
+
+## Output files
+
+By using the `-o` flag, you can specify your intended output file/directory.
+
+```bash
+$ transdoc input.txt -o output.txt
+...
+```
+
+## Other options
+
+* `--dryrun`: don't produce any output file(s). Just check for errors in the
+  inputs. This still evaluates all rules, so any side effects of rule
+  evaluation will still occur.
+* `--force`: always overwrite the output file/directory, regardless of whether
+  it contains data.
+* `-v`, `-vv`, `-vvv`: control verbosity of logging.
+* `--help`: show help information
+* `--version`: show version information
+
+### Additional notes
+
+You can disable the pride flags in the `--help` output by using the `NO_PRIDE`
+environment variable.