enable ccache by default on development shell

Author: mazunki

README.md

@@ -72,7 +72,7 @@ This will build the toolchain and all IncludeOS kernel libraries.
 
 Note that the first build will take some time (~7 hours on our machines) to complete, as the IncludeOS toolchain is rebuilt from source code. This includes clang, llvm, libcxx, musl and so on. There is no nix binary cache available for these files at the moment. Subsequent builds will go much faster when the toolchain has been cached in the local nix-store.
 
-After making changes to the kernel, run `nix-build` again to get new binaries. If you are iterating on changes in one section of the kernel you can speed up the build significantly (from a few minutes to a matter of seconds) by using ccache. All `nix-build` and `nix-shell` commands in this section support the optional parameter `--arg withCcache true`. We strongly advise setting up the ccache before you start iterating on the code. For NixOS, you can [check the wiki](https://nixos.wiki/wiki/CCache) on how to do this, other distros will have different instructions.
+After making changes to the kernel, run `nix-build` again to get new binaries. If you are iterating on changes in one section of the kernel you can speed up the build significantly (from a few minutes to a matter of seconds) by using ccache. All `nix-build` and `nix-shell` commands in this section support the optional parameter `--arg withCcache <true|false>` (this is only enabled by default for the development shell). We strongly advise setting up the ccache before you start iterating on the code. For NixOS, you can [check the wiki](https://nixos.wiki/wiki/CCache) on how to do this, other distros will have different instructions.
 
 ### <a name="develop_kernel"></a> Kernel development workflow
 It's not always practical to rebuild the whole kernel during development. You can get a development shell with a preconfigured environment using `develop.nix`:

develop.nix

@@ -10,7 +10,7 @@
   vmrunner ? "",
 
   # Enable ccache support. See overlay.nix for details.
-  withCcache ? false,
+  withCcache ? true,
 
   # Enable multicore suport.
   smp ? false,