Update README.md

README.md

-# pubMedCrawler
+# PUBMED API Crawler
 
 ## API documentation
+https://www.ncbi.nlm.nih.gov/books/NBK25501/
 
-https://www.ncbi.nlm.nih.gov/books/NBK25501/
\ No newline at end of file
+## Usage
+### Entry function
+The basic entry point of this crawler is the function `PUBMED.` `getMetadataWith`.
+
+This function take a `Text` representing the query you want to run on hal
+and a `Maybe Int` representing the maximum number of result you want to get.
+### Return Type
+The return type is a bit more tricky, it's **either** a `Text` representing an error or a collection of `PUBMED.Parser` `PubMed`.
+
+`PubMed` is a simple type that contain every informations we need (id,title,abstract,publicationDate,sources).
+
+### Exemple
+Here is a basic main using the entry point of the crawler and printing the 5 first documents.
+```hs
+{-# LANGUAGE OverloadedStrings #-}
+
+module Main where
+
+import PUBMED (getMetadataWith)
+
+
+main :: IO ()
+main = getMetadataWith "bisphenol" (Just 5) >>= print
+
+```
+