Build docs: make clear that installation paths should be adjusted

For a regular "user" build, the default installation paths aren't really
suitable (and are unusuable on MacOS for example due to its SIP
feature). Make it clear that appropriate paths should be chosen.

BUILD

@@ -2,39 +2,49 @@ Building Dinit
 =-=-=-=-=-=-=-
 
 Building Dinit should be a straight-forward process. It requires GNU make and a C++11 compiler
-(GCC version 4.9 and later, or Clang ~5.0 and later, should be fine).
+(GCC version 4.9 and later, or Clang ~5.0 and later, should be fine), as well as a handful of
+utilities that should be available on any POSIX-compliant system; in particular, the "m4"
+processor is required for the manual pages.
 
 
 Short version
 =-=-=-=-=-=-=
 
-Run "make" (or "gmake" if that is GNU make on your system). Your system type will hopefully be
-detected automatically and appropriate configuration chosen, and Dinit will be built. Continue
-reading instructions at "Running the test suite" or skip straight to "Installation".
+Run "make mconfig" (use "gmake mconfig" if GNU make is installed as "gmake"). Edit the generated
+"mconfig" file to your liking; typically you will want to adjust SBINDIR and MANDIR, which control
+the installation paths for executable files and  man pages respectively.
 
-If this fails, or if you are cross-compiling, read the "long version" instructions.
+Run "make"/"gmake" to build. Your system type will hopefully be detected automatically and
+appropriate configuration chosen, and Dinit will be built. Continue reading instructions at
+"Running the test suite" or skip straight to "Installation".
+
+If you run into any problems, or if you are cross-compiling, read the "long version" instructions.
 
 
 Long version 
 =-=-=-=-=-=-
 
-On the directly supported operating systems - Linux, OpenBSD, FreeBSD and Darwin (macOS) - a
-suitable build configuration is provided and will be used automatically if no manual configuration
-is supplied - skip directly to running "make" (more details below) if you are on one of these
-systems and are happy to use the default configuration.
+On the directly supported operating systems - Linux, OpenBSD, FreeBSD and Darwin (including
+macOS) - a suitable build configuration is provided and will be used automatically if no manual
+configuration is supplied - skip directly to running "make" (more details below) if you are on one
+of these systems and are happy to use the default configuration, but note that you will typically
+at least want to alter the installation location.
+
+If you are using a different system, or want to alter the default configuration, first run "make
+mconfig" to generate the "mconfig" file which contains the build configuration. You can then edit
+this file by hand, before proceeding with the build.
 
-For other systems, the "configure" script will run and try to generate a suitable "mconfig" file
-which specifies the build configuration. If you would prefer, you can run configure yourself
-before running "make"; this allows you to specify various options and/or hand-edit the generated
-mconfig file.
+An alternative to "make mconfig" is to use the provided "configure" script. It will try to
+generate a suitable "mconfig" file, based on sensible defaults and options provided on the command
+line when the script is run.
 
 For more information on available options from the configure script, run:
 
     ./configure --help
 
-As an alternative to running "configure", you can create and edit the "mconfig" file completely by
-hand (or start by copying one for a particular OS from the "configs" directory) to choose
-appropriate values for the configuration variables defined within. In particular:
+You can also create and edit the "mconfig" file completely by hand (or start by copying one for a
+particular OS from the "configs" directory) to choose appropriate values for the configuration
+variables defined within. In particular:
 
   CXX      : should be set to the name of the C++ compiler (and link driver)
   CXXFLAGS : are options passed to the compiler during compilation
@@ -86,7 +96,7 @@ to specify additional options without removing the defaults):
     TEST_LDFLAGS_EXTRA   : additional options to use when linking tests
 
    
-Recommended Compiler options
+Recommended compiler options
 =-=-=-=-=-=-=-=-=-=-=-=-=-=-
 
 Dinit should generally build fine with no additional options, other than:
@@ -150,8 +160,8 @@ DEFAULT_STOP_TIMEOUT=XXX
     via the service description).
 
 
-Running test suite
-=-=-=-=-=-=-=-=-=-
+Running the test suite
+=-=-=-=-=-=-=-=-=-=-=-
 
 Build the "check" target in order to run the test suite:
 
@@ -211,6 +221,9 @@ DESTDIR:
 The dinit executable will be put in /sbin (or rather, in $DESTDIR/sbin), which may not be on the
 path for normal users. Consider making a symbolic link to /usr/sbin/dinit.
 
+Note that if you specify installation paths via variables on the "make" command line, you should
+specify the same values for both build and install steps.  
+
 
 Special note for GCC/Libstdc++
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