chore(repo): add readme

README.md

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+# kubeprobes
+
+Simple and effective package for implementing [Kubernetes liveness and readiness probes](https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-probes/)' handler.
+
+## Installation
+
+```bash
+go get -u pkg.icikowski.pl/kubeprobes
+```
+
+## Usage
+
+The package provides `kubeprobes.New` function which returns a probes handler compliant with `http.Handler` interface.
+
+The handler serves two endpoints, which are used to implement liveness and readiness probes by returning either `200` (healthy) or `503` (unhealthy) status:
+
+- `/live` - endpoint for liveness probe;
+- `/ready` - endpoint for readiness probe.
+
+Accessing any other endpoint will return `404` status. In order to provide maximum performance, no body is ever returned.
+
+The `kubeprobes.New` function accepts following options-applying functions as arguments:
+
+- `kubeprobes.WithLivenessProbes(/* ... */)` - adds particular [probes](#probes) to the list of liveness probes;
+- `kubeprobes.WithReadinessProbes(/* ... */)` - adds particular [probes](#probes) to the list of readiness probes.
+
+## Probes
+
+In order to determine the state of particular element of application, probes need to be implemented either by creating [status determining function](#probe-functions) or by using simple and thread-safe [stateful probes](#stateful-probes).
+
+### Probe functions
+
+Probe functions (objects of type `ProbeFunction`) are functions that performs user defined logic in order to determine whether the probe should be marked as healthy or not. Those functions should take no arguments and return error (if no error is returned, the probe is considered to be healthy; if error is returned, the probe is considered to be unhealthy).
+
+```go
+someProbe := func() error {
+    // Some logic here
+    if somethingIsWrong {
+        return errors.New("something is wrong")
+    }
+    return nil
+}
+
+someOtherProbe := func() error {
+    // Always healthy
+    return nil
+} 
+
+// Use functions in probes handler
+kp := kubeprobes.New(
+    kubeprobes.WithLivenessProbes(someOtherProbe),
+    kubeprobes.WithReadinessProbes(someProbe),
+)
+```
+
+### Stateful probes
+
+Stateful probes (objects of type `StatefulProbe`) are objects that can be marked either as "up" (healthy) or "down" (unhealthy) and provide a `ProbeFunction` for easy integration. Those objects utilize `sync.Mutex` mechanism to provide thread-safety.
+
+```go
+// Unhealthy by default
+someProbe := kubeprobes.NewStatefulProbe()
+someOtherProbe := kubeprobes.NewStatefulProbe()
+
+// Use it in probes handler
+kp := kubeprobes.New(
+    kubeprobes.WithLivenessProbes(someProbe.GetProbeFunction()),
+    kubeprobes.WithReadinessProbes(someOtherProbe.GetProbeFunction()),
+)
+```
+
+## Example usage
+
+```go
+// Create stateful probes
+live := kubeprobes.NewStatefulProbe() 
+ready := kubeprobes.NewStatefulProbe()
+
+// Prepare handler
+kp := kubeprobes.New(
+    kubeprobes.WithLivenessProbes(live.GetProbeFunction()),
+    kubeprobes.WithReadinessProbes(ready.GetProbeFunction()),
+)
+
+// Start the probes server
+probes := &http.Server{
+    Addr:    ":8080",
+    Handler: kp,
+}
+go probes.ListenAndServe()
+
+// Mark probes as healthy
+live.MarkAsUp()
+ready.MarkAsUp()
+```