Add all missing functions to "Usage" introduction in README.md

Also, add links to all sections for each of those functions.

Author: Electronic-Mango

README.md

@@ -47,12 +47,16 @@ pip install simple-justwatch-python-api
 
 ## Usage
 
-This Python API has 3 functions:
-
- - `search` - search for entries based on title
- - `details` - get details for entry based on its node ID
- - `offers_for_countries` - get offers for entry based on its node ID, can look for offers
-   in multiple countries
+This Python API has multiple functions:
+
+ - [`search`](#search) - search for entries based on title
+ - [`popular`](#popular) - get a list of currently popular titles
+ - [`details`](#details) - get details for entry based on its node ID
+ - [`seasons`](#seasons) - get information about all seasons of a show
+ - [`episodes`](#episodes) - get information about all episodes of a season
+ - [`offers_for_countries`](#offers-for-countries) - get offers for entry based on its node ID,
+   can look for offers in multiple countries
+ - [`providers`](#providers) - get data about available providers (e.g., Netflix)
 
 Detailed documentation is available in https://electronic-mango.github.io/simple-justwatch-python-api/.