doc: Add usage examples

README.md

@@ -5,6 +5,9 @@ Swiss knife for ical & caldav calendars
 
 ## Roadmap
 
+Read a calendar
+
+
 Access to calendar
 
 * :x: access to public calendar
@@ -39,8 +42,54 @@ Serve calendar locally
 
 * :x: provide caldav urls for generated calendars
 
+## 
+
+Find free time
+
+    kiwimix generate \
+        --from-date XXX --to-date YYY \
+        --from-time 9:00 --to-time 19:00 \
+        | kiwimix substract - agenda.ics \
+
+Find free time for a meeting
+
+    kiwimix generate \
+        --from-date XXX --to-date YYY \
+        --from-time 9:00 --to-time 19:00 \
+        > full.ics
+    kiwimix union alice.ics bob.ics \
+        > events.ics
+    kiwimix substract full.ics events.ics \
+        > free.ics
+
+Rewrite events
+
+    kiwimix filter --merge alice.ics \
+      | kiwimix filter --anonymize - \
+
+
+V2 (with stack support)
+
+    kiwimix 
+      generate --....     # generate X calendar & push
+      @ read alice          # push alice.ics 
+      @ filter --merge      # pop alice, filter & push
+      @ filter --anonymize  # pop alice, filter & push
+      @ read bob            # push bob.ics 
+      @ filter --merge      # pop bob, filter & push
+      @ filter --anonymize  # pop bob, filter & push
+      @ union               # pop bob, pop alice, compute alice - bob
+      @ substract           # pop bob, pop alice, compute alice - bob
+
+
+    kiwimix filter --anonymize --merge alice.ics
+    kiwimix load bob.ics ! anonymize ! merge
 
 ## References
 
+* https://github.com/PuloV/ics-golang => features missing but the code is OK
+* https://github.com/apognu/gocal => poorly coded
 * https://github.com/samedi/caldav-go
 * https://github.com/emersion/go-webdav
+
+