(svn r17165) -Update: tweak obs/obg format description slightly

docs/obg_format.txt

@@ -49,6 +49,8 @@ tropical     = TRGH.GRF
 ; GRF file with extra toyland sprites
 toyland      = TRGT.GRF
 ; NewGRF file using Actions 5, 7, 9 and A to replace sprites
+; Must use a GRF ID starting with FF so it cannot be selected from
+; the in-game NewGRF list and (thus) be loaded twice.
 extra        = OPENTTDD.GRF
 
 ; The md5s section lists the MD5 checksum for the files that replace them.

docs/obs_format.txt

@@ -36,7 +36,7 @@ description  = foo
 ; The files section lists the files that replace sprites.
 ; The file names are case sensitive.
 [files]
-; file with the samples
+; The file with the samples. Must contain exactly 73 samples.
 samples      = SAMPLES.CAT
 
 ; The md5s section lists the MD5 checksum for the files that replace them.