add const documentation

resources/weight_analyzer/src/lib.rs

@@ -11,10 +11,15 @@ use subweight_core::parse::storage::Weights;
 use subweight_core::scope::Scope;
 use subweight_core::term::Term;
 
+// Substrate default maximum weight of a block in nanoseconds.
+// Since the maximum block weight is one-third of the execution time,
+// it corresponds to a block time of 6 seconds.
+const MAX_BLOCK_WEIGHT_NS: f64 = 2_000_000_000_000.;
+
 pub struct MaxBlockWeight(f64);
 impl Default for MaxBlockWeight {
     fn default() -> Self {
-        MaxBlockWeight(2_000_000_000_000.)
+        MaxBlockWeight(MAX_BLOCK_WEIGHT_NS)
     }
 }
 impl Div<&MaxBlockWeight> for f64 {