fix markdownlint errors: emphasis style, heading increment

Author: floxrox

docs/concepts/priority.md

@@ -198,7 +198,7 @@ not a file-level priority collision.
 
 After merging,
 the resulting environment is built
-and any file-level collisions between *different* packages
+and any file-level collisions between _different_ packages
 are resolved by priority
 the same way they are in a non-composed environment.
 

docs/tutorials/vendoring-dependencies.md

@@ -17,7 +17,7 @@ you use:
 There are two distinct vendoring problems you may encounter,
 and these call for different solutions.
 
-### Sandbox vendoring vs. missing dependencies
+## Sandbox vendoring vs. missing dependencies
 
 **Sandbox vendoring** is when your dependencies exist in their language
 ecosystem (Go modules, crates.io, npm) but a