detect-environment: Document the detect_tools function

Ticket: ENT-12600
Signed-off-by: Lars Erik Wik <lars.erik.wik@northern.tech>

Author: larsewi

build-scripts/detect-environment

@@ -331,6 +331,9 @@ detect_arch()
   export ARCH
 }
 
+# This function detects the path to various tools needed by the build system.
+# It's useful if the specified tool is not in PATH, or if the PATH resolution
+# picks up the wrong tool, or if e.g. gmake is preferred over make.
 detect_tools()
 {
     # We look for GNU Make because
@@ -345,9 +348,12 @@ detect_tools()
         exit 42
     fi
 
+    # fuser displays the PIDs of processes using specified files or file
+    # systems. We use it to kill processes that can mess with the build process.
     FUSER=$(func_whereis fuser)
     export FUSER
 
+    # We use it to submit patches to the dependencies.
     PATCH=$(func_whereis gpatch patch)
     export PATCH
 }