Add README

Signed-off-by: Knut Ahlers <knut@ahlers.me>

README.md

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+# Luzifer / worktime
+
+Worktime is intended as a personal time tracker for cases where the employer trusts you to work the amount of hours set in your contract but you want to make sure you really did.
+
+## Usage
+
+```bash
+# worktime help
+Manage worktimes in CouchDB
+
+Usage:
+  worktime [command]
+
+Available Commands:
+  overtime    Shows total overtime over all time
+  show        Display a summary of the given / current day
+  tag         Adds or removes a tag from the day or time entry inside the day
+  time        manipulate times of a day
+
+Flags:
+      --config string    config file (default is $HOME/.worktime.yaml)
+      --couchdb string   URL to access couchdb (http://user:pass@host:port/database)
+```
+
+## Setup
+
+You will need:
+
+- The worktime binary (see [latest release](https://github.com/Luzifer/worktime/releases/latest))
+- A [CouchDB](https://couchdb.apache.org/) instance already set up with a database
+- One design document (`analysis`) with (at least) one view (`overtime`) in it (see below for an example)
+
+After you've set up all of this you will need to export the `COUCHDB` environment variable in the form `https://user:pass@host/db` when using the `worktime` commandline tool. (Alternatively you could pass the `--couchdb` commandline flag to worktime every time you call it)
+
+### Example of required view
+
+This view (`analysis/overtime`) does the time calculation for you so you definitely need to adjust that one for your personal needs (weekly hours, tags, ...).
+
+**Map Function**
+
+```javascript
+function(day) {
+  var hasTag = function(day, tag) { return day.tags && day.tags.indexOf(tag) > -1 }
+
+  var worked_time = 0.0;
+  var daily_hours = 8.0;
+
+  for (var idx = 0; idx < day.times.length; idx++) {
+    var time = day.times[idx];
+    var s = new Date(day._id + 'T' + time.start);
+    var e = new Date(day._id + 'T' + time.end);
+    var diff = (e - s) / 1000.0 / 3600.0;
+    
+    if (hasTag(time, "break")) {
+      worked_time = worked_time - diff;
+    } else {
+      worked_time = worked_time + diff;
+    }
+  }
+  
+  if (hasTag(day, "holiday") || hasTag(day, "vacation") || hasTag(day, "ill") || hasTag(day, "weekend")) {
+    required_time = 0.0;
+  } else {
+    required_time = daily_hours;
+  }
+  
+  var outcome = worked_time - required_time;
+  
+  emit(day._id, outcome);
+}
+```
+
+**Reduce Function**
+
+```javascript
+function(keys, values, rereduce) {
+  var sum = 0.0;
+  for(var idx = 0; idx < values.length; idx++) {
+    sum = sum + values[idx];
+  }
+  
+  return sum;
+}
+```
+
+Of course this does not need to be the only view: You can for example add a view to count your days of vacation or even any other evaluation you can imagine. The tool just relies on `analysis/overtime` to be present.