Add placeholder for cylinder type description

So we don't want to save working pressure, but cylinder type knowledge
would be lovely and useful.  And we can probably make a good initial
guess, or at least let people fill it in later.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

dive.h

@@ -75,6 +75,7 @@ typedef struct {
 typedef struct {
 	volume_t size;
 	pressure_t workingpressure;
+	const char *description;	/* "LP85", "AL72", "AL80", "HP100+" or whatever */
 } cylinder_type_t;
 
 typedef struct {