(re)structured INSTALL.md and transformed into markdown; added hint t…

…hat installation into prefix has to be done with DESTDIR make variable and that there's no prefix support in configure, close iputils#21

INSTALL.md

@@ -1,24 +1,26 @@
-
-make
-make html
-make man
-lynx doc/iputils.html
-Read...
-
-
-
-If the first "make" fails, no problems:
-
-make html
-lynx doc/iputils.html
-Read section "Installation notes"...
-
-
-
-But if "make html" fails too, check that DocBook package is installed
-on your machine. If it is installed, and nevertheless "make" does not work,
-delete iputils and go to sleep. The next day repeat. If even full reset
-did not help, I bring apologies. :-)
-
-
+# Installation instructions
+Run the following commands:
+
+    make
+    make html
+    make man
+    lynx doc/iputils.html
+    # Read...
+
+## Troubleshooting
+If the first `make` fails, no problems:
+
+    make html
+    lynx doc/iputils.html
+    Read section "Installation notes"...
+
+But if `make html` fails too, check that DocBook package is installed
+on your machine. If it is installed, and `make` does not work nevertheless,
+please [open an issue on github.com]
+(https://github.com/iputils/iputils/issues/new).
+
+## Install into a prefix
+There's no `configure` option to install into a prefix. Use the `DESTDIR` 
+`make` variable to change the installation target. There's no support for 
+picking up build dependencies in a prefix.