Apply suggestions from code review

Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>

doc/manual/src/contributing/hacking.md

@@ -150,7 +150,7 @@ Add more [system types](#system-type) to `crossSystems` in `flake.nix` to bootst
 
 It is useful to perform multiple cross and native builds on the same source tree,
 for example to ensure that better support for one platform doesn't break the build for another.
-In order to facilitate this for, Nix has some support for being built out of tree:
+In order to facilitate this, Nix has some support for being built out of tree – that is, placing build artefacts in a different directory than the source code:
 
 1. Create a directory for the build, e.g.
 
@@ -162,13 +162,13 @@ In order to facilitate this for, Nix has some support for being built out of tre
 
    ```bash
    cd build
-   ../configure ...configure-flags
+   ../configure <configure flags>
    ```
 
 3. Run make from the source directory, but with the build directory specified, e.g.
 
    ```bash
-   make builddir=build ...make-flags
+   make builddir=build <make flags>
    ```
 
 ## System type