Create README.md

README.md

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+# go-cache
+
+Simple thread safe key/value cache for Go.
+
+## Usage
+
+You can initialize the cache using:
+
+```go
+    cache = gocache.NewCache()
+```
+
+And perform the operations using:
+
+```go
+   // GET a value using key, which returns (value, error)
+   cache.Get(key)
+   
+   // SET a value using key
+   cache.Set(key, value)
+   
+   // REMOVE a key/value pair using key
+   cache.Remove(key)
+   
+   // And FLUSH, which removes all items from the cache
+   cache.Flush()
+```
+
+## Cache Expiration
+
+You can also add an **expiration** to the cache, expired cache will be auto deleted by the `sweeper`.
+
+To initialize a cache using `sweeper` we can use:
+
+```go
+    cache := NewCacheWithSweeper(10 * time.Minute, 10 * time.Minute, decisionFunc, onEviction)
+```
+
+Here, first two parameters are `interval` and `expireAfter`, sweeper will run in the background after specified `interval` to check for expired cache to delete.
+
+The `decisionFunc` and `onEviction` are **optional** functions with the following signature:
+```go
+    decisionFunc func(v interface{}) bool
+    
+    onEviction func(k string, v interface{})
+```
+
+We can use `decisionFunc` as a callback, it will be called by the cache before deleting a key/value, it takes in the value to delete and returns `true` to delete and `false` for not deleting a key/value pair even after expired.
+
+The `onEviction` is a callback which will be called every time a cache is deleted with its key/value as parameters.