Mention the Nix binary cache for faster builds. (#2085)

* Mention the Nix binary cache for faster builds.

See #1074.

* Use proper markdown-syntax for links

Co-authored-by: rv-jenkins <admin@runtimeverification.com>

Author: RaoulSchaffranek

README.md

@@ -33,7 +33,7 @@ The rest of this file assumes you intend to build and install the K Framework
 from source.
 
 Note that the K Framework can only be built on (x86-64) Linux-like systems,
-e.g., this also includies macOS/brew (x86-64) as well as the Windows Subsystem
+e.g., this also includes macOS/brew (x86-64) as well as the Windows Subsystem
 for Linux.
 All 32-bit systems are **not supported**.
 See the
@@ -186,6 +186,11 @@ should be installed.
 
 ## Building with Nix
 
+By default, Nix will build the project and its transitive dependencies from
+source, which can take up to an hour. We recommend setting up
+[the binary cache](https://app.cachix.org/cache/kore) to speed up the build
+process significantly.
+
 To build the K Framework itself, run:
 
 ```bash