Add FAQ entry about --headers values

Be as clear as possible about what the --headers command-line option
or headers configuration option does, and what sorts of values are
valid for it.

diff --git a/FAQ b/FAQ
index 1e0ff03..280c0af 100644 (file)
--- a/FAQ
+++ b/FAQ
@@ -2,7 +2,7 @@
  Frequently Asked Questions About the Weather Utility
 ======================================================
 
  Frequently Asked Questions About the Weather Utility
 ======================================================
 

-:Copyright: (c) 2006-2012 Jeremy Stanley <fungi@yuggoth.org>. Permission
+:Copyright: (c) 2006-2017 Jeremy Stanley <fungi@yuggoth.org>. Permission

             to use, copy, modify, and distribute this software is
             granted under terms provided in the LICENSE file distributed
             with this software.
             to use, copy, modify, and distribute this software is
             granted under terms provided in the LICENSE file distributed
             with this software.


@@ -54,3 +54,25 @@ As of the 2.0 release, this question is no longer relevant.
 ---------------------------------------------------------------
 As of the 2.0 release, this is no longer necessary. See FAQ entries #2
 and #3 for more detail.
 ---------------------------------------------------------------
 As of the 2.0 release, this is no longer necessary. See FAQ entries #2
 and #3 for more detail.

+
+7. What values are valid for a --headers list?
+----------------------------------------------
+The default set it uses if you don't override it yourself on the command
+line or in configuration is as follows::
+
+  heat_index
+  precipitation_last_hour
+  relative_humidity
+  sky_conditions
+  temperature
+  weather
+  wind
+  windchill
+
+These are a case-insensitive match against the start of lines in a
+decoded METAR up to the first colon (:) with underscores (_) replaced by
+spaces. You can see the full METAR for a given condition report by
+passing --verbose or by observing one directly (perhaps by looking in
+your *datacache* directory). Unfortunately I haven't found any proper
+specification for the decoded METAR format used by the NWS so know of no
+comprehensive list of what lines might appear.