tried out obsidian, started ch 6.2

Constants.md

@@ -0,0 +1,11 @@
+# Constants
+
+- Can be declared anywhere,
+- The convention to use all caps in a constant's name
+- Needs const keyword
+- Not always evaluated at compile time (there are rules for this but too complex to know everything)
+- Variables can only be assigned once (needs mut to assign more than once (need to be same type))
+
+```rust
+const SECONDS_PER_HOUR: i32 = 60 * 60;
+```