OS (Linux): detect detailed debian version

Ref: https://github.com/dylanaraps/neofetch/issues/2381

src/detection/os/os_linux.c

@@ -1,6 +1,7 @@
 #include "os.h"
 #include "common/properties.h"
 #include "common/parsing.h"
+#include "common/io/io.h"
 #include "util/stringUtils.h"
 
 #include <string.h>
@@ -121,6 +122,14 @@ static void getUbuntuFlavour(FFOSResult* result)
     }
 }
 
+static void getDebianVersion(FFOSResult* result)
+{
+    FF_STRBUF_AUTO_DESTROY debianVersion = ffStrbufCreate();
+    ffAppendFileBuffer("/etc/debian_version", &debianVersion);
+    if (debianVersion.length)
+        ffStrbufSet(&result->version, &debianVersion);
+}
+
 static void detectOS(FFOSResult* os)
 {
     if(instance.config.osFile.length > 0)
@@ -169,6 +178,8 @@ void ffDetectOSImpl(FFOSResult* os)
 
     detectOS(os);
 
-    if(ffStrbufIgnCaseCompS(&os->id, "ubuntu") == 0)
+    if(ffStrbufIgnCaseEqualS(&os->id, "ubuntu"))
         getUbuntuFlavour(os);
+    else if(ffStrbufIgnCaseEqualS(&os->id, "debian"))
+        getDebianVersion(os);
 }