README.md in calrom-0.2.0 vs README.md in calrom-0.3.0

@@ -44,20 +44,82 @@
 
 ... for an arbitrary date range:
 
 `$ calrom 2028-01-15 2028-03-07`
 
+### Selecting calendar
+
+There are a few calendars bundled in calrom (actually in the calendarium-romanum gem)
+and ready to use. List them:
+
+`$ calrom --calendars`
+
+Each entry of the listing contains an ID of the calendar, it's name and language code.
+Use calendar ID to request General Roman Calendar in Latin:
+
+`$ calrom --calendar=universal-la`
+
+You can prepare [your own calendar data][carodata] and load them:
+
+`$ calrom --calendar=path/to/my_calendar.txt`
+
+If you specify more than one calendar, they are loaded "layered" one over another
+(from left to right), which comes in handy when extending a general calendar
+with just a few additional and/or differing celebrations, e.g. solemnities (titular, dedication)
+of the local church:
+
+`$ calrom --calendar=universal-la --calendar=path/to/our_local_celebrations.txt`
+
 ### Data presentation settings
 
 Print detailed listing:
 
 `$ calrom -l`
 
 Disable colours:
 
 `$ calrom --no-color`
 
+Machine-readable output formats:
+
+`$ calrom --format=json` - prints JSON array containing one object per day.
+The object contents mimick output of the [Church Calendar API v0][calapidoc].
+
+`$ calrom --format=csv` - prints a CSV, one celebration per line
+(i.e. there is one or more lines for each liturgical day).
+
+### Configuration files
+
+`calrom` looks for configuration files `/etc/calromrc` and `~/.calromrc`.
+They are processed in this order and both are used if available.
+Their syntax is that of shell options and arguments (with the sole exception that newline
+is not considered end of shell input, but generic whitespace), supported are all options and arguments
+accepted by the command.
+It usually makes sense to use configuration files only for the most fundamental settings
+you will never change, like selecting calendar (if you know you will always check this single one)
+or disabling colours (if you hate colourful output).
+
+If a custom configuration file location is specified on the command line,
+`$ calrom --config=path/to/my/custom/config`, the standard system-wide and user-specific configuration
+files are *not* loaded.
+
+Example configuration file, loading the proper calendar of the archdiocese of Prague
+and disabling colours:
+
+```bash
+# shell-like comments can be used in configuration files
+
+--calendar=czech-cs       # celebrations common for the whole Czech Republic
+--calendar=czech-cechy-cs # Bohemia
+--calendar=czech-praha-cs # archdiocese of Prague
+--calendar=/home/igneus/calendar_data/local_church.txt # path to a custom calendar file with proper celebrations of the parish where I live (titular feast of the church, dedication)
+
+--no-color # disable colours
+```
+
+(Configuration file format is inspired by [.rspec][dotrspec].)
+
 ## Running tests
 
 Clone the repository, `$ bundle install` to install dependencies, then:
 
 `$ rake cucumber` - run specs describing the command line interface
@@ -67,18 +129,18 @@
 `$ rake` - run all groups of specs one after another
 
 ## Project roadmap
 
 * [x] detailed listing of a day/month/year/range of dates
-* [ ] month/year overview - options and output mostly mimicking the
+* [ ] month/year overview - options and output mostly mimicking
   the BSD Unix [`cal`][cal] utility,
   but with liturgical colours and celebration ranks
 * [ ] condensed format (but with detailed information) suitable for awesome/i3 toolbars etc.
-* [ ] machine-readable detailed listing
+* [x] machine-readable detailed listing
 * [ ] year summary: lectionary cycles, movable feasts
-* [ ] configuration file to set default options
-* [ ] specify calendar data path (with support for layering several calendars)
+* [x] configuration file to set default options
+* [x] specify calendar data path (with support for layering several calendars)
 * [ ] option to auto-select one of optional celebrations - with multiple supported strategies (prefer ferial, take first non-ferial, configured whitelist, blacklist)
 * [ ] integrate online data sources
 * [ ] interactive browsing
 
 ## Backward compatibility
@@ -112,8 +174,11 @@
 ## License
 
 GNU/GPL 3.0 or later
 
 [caro]: https://github.com/igneus/calendarium-romanum
+[carodata]: https://github.com/igneus/calendarium-romanum/tree/master/data
+[calapidoc]: http://calapi.inadiutorium.cz/api-doc
 [semver]: https://semver.org/
 [cal]: https://www.freebsd.org/cgi/man.cgi?query=cal
 [taoup]: http://www.catb.org/esr/writings/taoup/html/ch10s05.html
+[dotrspec]: https://relishapp.com/rspec/rspec-core/v/2-0/docs/configuration/read-command-line-configuration-options-from-files