added hooks readme with usage codesnippets

hooks/README.md

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+# Usage
+
+## Network
+React hook for getting network status (effective connection type)
+
+```
+import { useEffectiveConnectionType } from './network';
+
+const MyComponent = () => {
+  const effectiveConnectionType = useEffectiveConnectionType();
+
+  let media;
+  switch(effectiveConnectionType) {
+    case 'slow-2g':
+      media = <img className="responsive" src="…" alt="low resolution" />;
+      break;
+    case '2g':
+      media = <img className="responsive" src="…" alt="medium resolution" />;
+      break;
+    case '3g':
+      media = <img className="responsive" src="…" alt="high resolution" />;
+      break;
+    case '4g':
+      media = <video className="responsive" src="…" controls />;
+      break;
+    default:
+      media = <video className="responsive" src="…" controls />;
+      break;
+  }
+  
+  return <div>{media}</div>;
+};
+```
+
+## Memory
+React hook for getting memory status of the device
+
+```
+import { useMemoryStatus } from './memory';
+
+const MyComponent = () => {
+  const { overLoad } = useMemoryStatus();
+  return (
+    <div>
+      { overLoad ? <img src='...' /> : <video src='...' /> }
+    </div>
+  );
+};
+```
+
+## Device-class
+React hook for getting device-class whether it's light or heavy
+
+```
+import { useDeviceClass } from './device-class';
+
+const MyComponent = () => {
+  const deviceClass = useDeviceClass();
+  return (
+    <div>
+      { deviceClass === ‘light’ ? <img src='...' /> : <video src='...' /> }
+    </div>
+  );
+};
+```
+
+## Battery
+React hook for getting battery status
+
+```
+import { useBatteryStatus } from './battery';
+
+const MyComponent = () => {
+  const batteryStatus = useBatteryStatus();
+  return (
+    <div>
+      { batteryStatus.level > 0.75 ? <video src='...' /> : <img src='...' /> }
+    </div>
+  );
+};
+```