feat: cache + paths (#1)

- Added helper function `ExpandUser`
- Added basic cache impmentations for in-memory and file based caches.

Reviewed-on: #1
Co-authored-by: Felipe M. <me@fmartingr.com>
Co-committed-by: Felipe M. <me@fmartingr.com>

README.md

@@ -1,7 +1,25 @@
 # gotoolkit
 
+[![Go Reference](https://pkg.go.dev/badge/git.nakama.town/fmartingr/gotoolkit.svg)](https://pkg.go.dev/git.nakama.town/fmartingr/gotoolkit)
+
 A set of basic tools to develop Go applications.
 
+# Index
+
+- [Cache](#cache)
+- [Database](#database)
+- [Paths](#paths)
+- [Service & Servers](#service--servers)
+- [Template](#template)
+
+## Cache
+
+A basic cache engine to manage the cache of the application.
+
+```go
+cache := cache.NewMemoryCache()
+```
+
 ## Database
 
 A basic database engine to manage the connection to a database.
@@ -13,6 +31,14 @@ if err != nil {
 }
 ```
 
+## Paths
+
+A basic utility to manage the paths of the application.
+
+```go
+path := paths.ExpandUser("~/myapp")
+```
+
 ## Service & Servers
 
 A basic way to expose servers within one service.