Hide changed connection lines behind -v/--verbose

set_local_db/set_dot_env diffs can contain secrets (connection
strings), so printing them unconditionally on every up/down leaked
credentials to stdout. Default output is now a line-count summary;
pass -v/--verbose to see the actual before/after lines.

README.md

@@ -35,13 +35,14 @@ cargo install --path .
 ## Usage
 
 ```
-dev_tools <project> <up|down>
+dev_tools <project> <up|down> [-v|--verbose]
 ```
 
 | Argument | Description |
 |---|---|
 | `project` | Project key (matches `<PROJECT>_DIR` in the config, case-insensitive) |
 | `up` / `down` | Start or stop the environment |
+| `-v`, `--verbose` | Print the actual before/after lines changed in the env files (values may include secrets, e.g. connection strings). Without it, only a line count is printed. |
 
 ### Examples
 
@@ -51,6 +52,9 @@ dev_tools foo up
 
 # Stop it
 dev_tools foo down
+
+# See exactly which lines were changed
+dev_tools foo up -v
 ```
 
 ## What it does