[doc] INSTALL: improve list of dependencies

INSTALL.t2t

@@ -20,14 +20,23 @@ libraries installed:
 You also need support for POSIX threads, which should be provided by
 default by your system in most cases, and the GCC C++ compiler (g++)
 version 4.7 or above; the Clang C++ compiler (clang++) version 3.2 or
-above should also work in most cases.
+above should also work. Compilation of the C modules has been tested
+with GCC and Clang and should work with older versions of these
+compilers.
+
+The additional tools are also recommended:
+- ``perl``
+- ``pod2man`` (normally provided in the same package as //Perl//)
+- ``doxygen``
+- ``txt2tags``
 
 If you miss one or more of the requirements, the concerned modules will
-not be built, but the others can still be.
+not be built.
 
 OwlPS uses //CMake// as a build manager. You need to install it (package
-``cmake`` on most distributions), and you should install ``ccmake`` as
-well if it is not shipped with the main CMake package (package
+``cmake`` on most distributions) as well as the ``make`` tool if not
+readily available on your system. You should also install ``ccmake`` if
+it is not shipped with the main CMake package (package
 ``cmake-curses-gui`` on Debian).
 
 It is strongly advised to build out of the source tree, which can be
@@ -166,9 +175,9 @@ In the configuration (``make menuconfig``), you have to:
 + Select the components needed to build (press the <space> key to have a
   //M// or a //*//). For example:
   - in the //Libraries// menu, select //confuse// and //libiw//;
-  - in the //Base system// menu, //libpthread// and //librt// should now
-    be automatically selected (the latter is only needed for OwlPS
-    Positioner).
+  - in the //Base system// menu, select //libpthread// and //librt// if
+    they were not automatically selected (the latter is only needed for
+    OwlPS Positioner).
 
 
 Note that at the moment, //libclaw_tween// is not provided by the