Update readme

README.md

@@ -1,2 +1,40 @@
 # npm-offline-registry
 Supper simple NPM registry server for offline NPM install
+
+# Usage
+
+* install this npm mpdule
+
+  `npm i harish2704/npm-offline-registry`
+* Run local npm-registry server
+
+  `npm-offline-registry`
+  *OR*
+   `node node_modules/.bin/npm-offline-registry`
+
+* Now the server will run on [http://localhost:8080](http://localhost:8080)
+* use `http://localhost:8080/` as registry while doing npm install
+  - Either use `npm install --registry http://localhost:8080/ [package-name]...`
+  - Or permanently set config variable `npm config set registry http://localhost:8080/`
+
+
+# How it is working?
+
+* When ever we do `npm install` in normal condition, the `npm` tool will keep a cache directory of the files which was downloaded by `npm` tool.
+* Default location of this cache directory is `~/.npm` for UNIX machines
+* `npm-offline-registry` tool will serve the requests using the cached versions of the files.
+* If a package/version is not found on cache, it is fetched from main `npm` registry. Then is properly inserted in to npm's cache directory.
+
+# Dependencies
+
+Currently this tool is using following unix commands to manipulate npm's cache directory.
+
+* `wget` for downloading the content from main npm registry
+* `mkdir` with `-p` option
+* `tar` command with gzip uncompresion
+
+I believe all the above said tools will be available in a typical UNIX machine.
+
+# Configurations
+
+Please check config.js. All config values can be over-written by `environment-variables`