Add magic pattern file for pre-processed Flexpart input files

utils/READ.ME

+==============
+magic.flexpart
+==============
+
+Magic pattern file for pre-processed Flexpart input files. See
+magic(5) and file(1). Append this file to /etc/magic or run
+"file -m ./magic.flexpart <file>". Example:
+
+file -m ./magic.flexpart /tmp/EN16060521
+/tmp/EN16060521: Flexpart v9.3.1 pre-processed met input file nxmax=721 nymax=361 nuvzmax=138 nwzmax=138 nzmax=138

utils/magic.flexpart

+# Flexpart Pre-Processed Met input file
+0	string	FP_p-	Flexpart
+>5      string/7  >\3     v%s pre-processed met input file
+>>12     lelong  >0         nxmax=%d
+>>16     lelong  >0         nymax=%d
+>>20     lelong  >0         nuvzmax=%d
+>>24     lelong  >0         nwzmax=%d
+>>28     lelong  >0         nzmax=%d