docs: mark make commands with same format as elsewhere

This uses the same formatting for the make command examples as seen in
README.md.

Signed-off-by: Adrian Reber <[email protected]>

INSTALL.md

@@ -23,9 +23,9 @@ passed to the make command:
 Once CRIU is built one can easily setup the complete CRIU package
 (which includes executable itself, CRIT tool, libraries, manual
 and etc) simply typing
-
+```
     make install
-
+```
 this command accepts the following variables:
 
  * **DESTDIR**, to specify global root where all components will be placed under (empty by default);
@@ -36,17 +36,17 @@ this command accepts the following variables:
  * **LIBDIR**, to specify directory where to put libraries (guess the correct path  by default).
 
 Thus one can type
-
+```
     make DESTDIR=/some/new/place install
-
+```
 and get everything installed under `/some/new/place`.
 
 ## Uninstalling CRIU
 
 To clean up previously installed CRIU instance one can type
-
+```
     make uninstall
-
+```
 and everything should be removed. Note though that if some variable (**DESTDIR**, **BINDIR**
 and such) has been used during installation procedure, the same *must* be passed with
 uninstall action.