tests: add README.md for periph_timer

Moving test description from code to a separate README.md file to reduce
binary size to make the test fit on an arduino-uno.

tests/periph_timer/README.md

@@ -0,0 +1,17 @@
+# Periph Timer Test
+
+## About
+
+This application will test all configured peripheral timers of the target
+platform. For each timer, it will set each channel with an incrementing
+timeout: CH0 is set to 5ms, CH1 to 10ms, CH2 to 15ms and so on.
+
+## Expected Result
+
+The output should show that every channel fired after an evenly distributed
+amount of time, i.e. the diff values should be equal (with some jitter...).
+
+## Note
+
+This test does however **NOT** show whether the timeouts and diffs were correct
+in relation to the expected real-time; use e.g. tests/xtimer_msg for this.

tests/periph_timer/main.c

@@ -115,16 +115,6 @@ int main(void)
     int res = 0;
 
     puts("\nTest for peripheral TIMERs\n");
-    puts("This test will test all configured peripheral timers of the\n"
-         "targeted platform. For each timer, it will set each channel with\n"
-         "an incrementing timeout. CH0 set to 5ms, CH1 to 10ms, CH2 to 15ms\n"
-         "and so on.\n"
-         "In the output you should see that every channel fired, after an\n"
-         "evenly distributed amount of time -> the shown diff values should\n"
-         "be pretty much equal (to some jitter...)\n"
-         "This test does however NOT show, if the timeouts were correct in\n"
-         "relation to the expected real-time ~ use e.g. tests/xtimer_msg for\n"
-         "this.\n\n");
 
     printf("Available timers: %i\n", TIMER_NUMOF);