docs/feat: add stdin support via - filename

README.md

@@ -72,6 +72,14 @@ ical2rem [OPTION]… FILE…
 
 Output goes to stdout and can be redirected to a `.rem` file.
 
+Pass `-` as a filename to read from standard input. `-` may appear at most once,
+but can be freely mixed with regular files:
+
+```bash
+curl https://example.com/calendar.ics | ical2rem - > calendar.rem
+ical2rem work.ics - personal.ics > all.rem
+```
+
 ### Examples
 
 Convert a single calendar:
@@ -99,6 +107,11 @@ Strip all metadata lines from output:
 ical2rem --no-uuid --no-source --no-location --no-description --no-conference-url personal.ics
 ```
 
+Use stdin as input calendar:
+```bash
+curl https://example.com/calendar.ics | ical2rem - > calendar.rem
+```
+
 Override calendar name in `INFO` lines (single file only):
 ```bash
 ical2rem --source "Work" work.ics > work.rem
@@ -113,7 +126,7 @@ ical2rem --verbose personal.ics > personal.rem
 
 | Option | Description |
 |---|---|
-| `FILE…` | One or more `.ics` files to convert |
+| `FILE…` | One or more `.ics` files to convert; use `-` for standard input (at most once) |
 | `-z`, `--timezone TZ` | Target timezone for output (default: local) |
 | `--sort asc\|desc\|original` | Sort order by date (default: `desc`); `original` preserves processing order (sorted by UID within each file, last file first) |
 | `--source NAME` | Override calendar name (single file only) |