Update compilation instructions throughout our docs

related to https://github.com/i3/i3/issues/4086

docs/hacking-howto

@@ -23,8 +23,10 @@ outdated information.
 
 == Building i3
 
-You can build i3 like you build any other software package which uses meson.
-Here’s a memory refresher:
+You can build i3 like you build any other software package which uses
+https://mesonbuild.com/[The Meson Build system]; see
+https://mesonbuild.com/Quick-guide.html#compiling-a-meson-project[Quickstart
+Guide → Compiling a Meson project]. In case you’re unfamiliar:
 
     $ mkdir -p build && cd build
     $ meson ..

docs/testsuite

@@ -120,13 +120,11 @@ tests are run under Xvfb.
 ---------------------------------------
 $ cd ~/i3
 
-$ autoreconf -fi
-
 $ mkdir -p build && cd build
 
-$ ../configure
+$ meson ..
 
-$ make -j8
+$ ninja
 # output omitted because it is very long
 
 $ cd testcases
@@ -183,13 +181,11 @@ You can still use ./testcases/complete-run.pl to get the interactive progress ou
 ---------------------------------------
 $ cd ~/i3
 
-$ autoreconf -fi
-
 $ mkdir -p build && cd build
 
-$ ../configure
+$ meson ..
 
-$ make -j8
+$ ninja
 # output omitted because it is very long
 
 $ make check