README.md : make things easier to understand after a private email discussion

Author: René Ladan

README.md

@@ -16,7 +16,8 @@ The software comes with three binaries and a library:
 * dcf77pi : Live decoding from the GPIO pins in interactive mode. Useable keys
   are shown at the bottom of the screen. The backspace key can be used to
   correct the last typed character of the input text (when changing the name of
-  the log file).
+  the log file). Depending on the permissions of your GPIO device node (the
+  files in /dev), you might need to run this program as root or with sudo.
 * dcf77pi-analyze filename : Decode from filename instead of the GPIO pins.
   Output is generated in report mode.
 * readpin [-q] : Program to test reading from the GPIO pins and decode the
@@ -25,23 +26,25 @@ The software comes with three binaries and a library:
   * -q do not show the raw input, default is to show it.
 * libdcf77.so: The shared library containing common routines for reading bits
   (either from a log file or the GPIO pins) and to decode the date, time and
-  third party buffer. Both dcf77pi and dcf77pi-analyze use this library.  Header
+  third party buffer. Both dcf77pi and dcf77pi-analyze use this library. Header
   files to use the library in your own software are supplied.
 
 The meaning of the keywords in config.txt is:
 
-* pin           = GPIO pin number
+* pin           = GPIO pin number (0-65535)
 * iodev         = GPIO device number (FreeBSD only)
 * activehigh    = pulses are active high (1) or passive high (0)
-* freq          = sample frequency in Hz
+* freq          = sample frequency in Hz (10-155000)
 * summermonth   = month in which daylight saving time starts
 * wintermonth   = month in which daylight saving time ends
 * leapsecmonths = months (in UTC) in which a leap second might be inserted
 * outlogfile    = name of the output logfile which can be read back using
-  dcf77pi-analyze (default empty)
+  dcf77pi-analyze (default empty). The log file itself only stores the
+  received bits, but not the decoded date and time.
 
 Note that a value of 0 can be used for summermonth, wintermonth, or
 leapsecmonths to disallow daylight saving time changes or leap seconds.
+Otherwise use one or more values from 1 to 12.
 
 The end of the minute is noted by the absence of high pulses. An absence of low
 pulses probably means that the transmitter is out of range. Any other situation
@@ -55,3 +58,13 @@ Currently supporrted platforms:
 * FreeBSD, Linux: full support
 * Cygwin, MacOS, NetBSD: supported without GPIO communication for live decoding
 * Windows: only via Cygwin
+
+On Linux, you will have to install an (n)curses package development using your
+package manager to get the required header files and the .so library file.
+For example:
+% sudo apt-get install ncurses-devel
+
+To build and install the program into /usr/bin , the library into /usr/lib and
+the configuration file into /usr/etc/dcf77pi :
+% make PREFIX=/usr
+% sudo make install PREFIX=/usr