cc doc: add missing links

Author: bracevac

docs/_docs/reference/experimental/capture-checking/classifiers.md

@@ -16,7 +16,7 @@ like this:
 ```scala
   trait Control extends SharedCapability, Classifier
 ```
-The Gears library then defines a capability class `Async` which extends `Control`.
+The [Gears library](https://lampepfl.github.io/gears/) then defines a capability class `Async` which extends `Control`.
 
 ```scala
   trait Async extends Control

docs/_docs/reference/experimental/capture-checking/scoped-caps.md

@@ -28,7 +28,7 @@ in the function itself. In that alternative notation, the type of makeLogger wou
 ```scala
 makeLogger: ∀cap₁.(fs: FileSystem^{cap₁}): ∃cap₂. Logger^{cap₂}
 ```
-There's a connection with capture polymorphism here. `cap`s in function parameters behave like additional
+There's a connection with [capture polymorphism](polymorphism.md) here. `cap`s in function parameters behave like additional
 capture parameters that can be instantiated at the call site to arbitrary capabilities.
 
 The conventions for method types carry over to function types. A function type