feat: add property for available memory

docs/docs/segments/sysinfo.md

@@ -41,7 +41,9 @@ Display SysInfo.
 ### Properties
 
 - `.PhysicalTotalMemory`: `int` - is the total of used physical memory
-- `.PhysicalFreeMemory`: `int` - is the total of free physical memory
+- `.PhysicalAvailableMemory`: `int` - is the total available physical memory (i.e. the amount immediately available to processes)
+- `.PhysicalFreeMemory`: `int` - is the total of free physical memory (i.e. considers memory used by the system for any reason
+[e.g. caching] as occupied)
 - `.PhysicalPercentUsed`: `float64` - is the percentage of physical memory in usage
 - `.SwapTotalMemory`: `int` - is the total of used swap memory
 - `.SwapFreeMemory`: `int` -  is the total of free swap memory

src/segments/sysinfo.go

@@ -16,12 +16,13 @@ type SystemInfo struct {
 
 	Precision int
 	// mem
-	PhysicalTotalMemory uint64
-	PhysicalFreeMemory  uint64
-	PhysicalPercentUsed float64
-	SwapTotalMemory     uint64
-	SwapFreeMemory      uint64
-	SwapPercentUsed     float64
+	PhysicalTotalMemory     uint64
+	PhysicalAvailableMemory uint64
+	PhysicalFreeMemory      uint64
+	PhysicalPercentUsed     float64
+	SwapTotalMemory         uint64
+	SwapFreeMemory          uint64
+	SwapPercentUsed         float64
 	// cpu
 	Times float64
 	CPU   []cpu.InfoStat
@@ -57,6 +58,7 @@ func (s *SystemInfo) Init(props properties.Properties, env environment.Environme
 	memStat, err := mem.VirtualMemory()
 	if err == nil {
 		s.PhysicalTotalMemory = memStat.Total
+		s.PhysicalAvailableMemory = memStat.Available
 		s.PhysicalFreeMemory = memStat.Free
 		s.PhysicalPercentUsed = memStat.UsedPercent
 	}