Add some notes on usage and build (#1)

* Fix a typo in the Makefile
* Print out the unknown timezone in the example
* Add some more details on usage and the build
* More notes on the build and the IANA tz db
* Remove unnecessary spaces in the Makefile

Author: jdlambert

Makefile

@@ -1,16 +1,16 @@
 CC=gcc
 CFLAGS=-I.
-DEPS = zones.h
+DEPS=zones.h
 TAG=posix-tz-db
 
 .PHONY: all clean example docker
 
 all: zones.o zones.h zones.json zones.csv
 
-# zones.o intentionally does not depend on making zones.c, since zones.c requires the 
-# consistent build environment provided by Docker or Arch Linux, and would only get
-# actually need an update a couple times a year or so. zones.c is checked in to source
-# control though, so build it once when it gets updated, commit it, and you're good.
+# `zones.o` intentionally does not depend on making `zones.c`, since `zones.c` requires the 
+# consistent build environment provided by Docker or the latest Arch Linux, and would only 
+# actually need an update a few times a year or so. `zones.c` is checked in to source
+# control though, so build it when it gets updated, commit it, and you're good.
 zones.o: zones.h
 	$(CC) -c -o zones.o $(CFLAGS) zones.c
 

README.md

@@ -5,4 +5,14 @@ An embeddable mapping between [IANA Time Zone Database](https://www.iana.org/tim
 In this way, more user-friendly names can be used in a timezone-setting API, and
 timezone rules can be easily updated with a firmware upgrade.
 
+### Usage
+
+See `example/example.c` for an embedded use case.
+
 Provide user-facing clients with `zones.json` to have a shared timezone vocabulary with the embedded library.
+
+### Build
+
+Since the build is heavily environment-dependant, the Dockerfile provides a consistent build environment — latest Arch Linux. When the IANA timezone database updates (a few times a year, usually: see the latest version [here](https://www.iana.org/time-zones) and compare to the release name/date), just run `make` in the root directory to rebuild all the "data" build artifacts (`zones.c` etc.). These data build artifacts can be checked in to source control since they change so infrequently.
+
+If the IANA timezone database hasn't changed, you can just build `zones.o`, which isn't as sensitive to the build environment.

example/example.c

@@ -27,7 +27,7 @@ void print_local_time(const char *name) {
     strftime(strftime_buf, sizeof(strftime_buf), "%c", &timeinfo);
     printf("The current date/time in %s is: %s\n", name, strftime_buf);
   } else {
-    printf("Unknown timezone!\n");
+    printf("%s is not a known timezone!\n", name);
   }
 
 }
@@ -37,4 +37,4 @@ int main() {
   print_local_time("Asia/Shanghai");
   print_local_time("Europe/Lisbon");
   print_local_time("亚洲/武汉");
-}
+}