Update .env file documentation

Author: Milan Lukac

.env.example

@@ -33,9 +33,7 @@ The Zoo also provides analytics about how dependency usage and its versions evol
 
 - Create a database: `$ make migrate`
 - Create a superuser: `$ make superuser`
-- Create `.env` file based on `.env.example`
-  - Use gitlab/github tokens with read permissions
-  - Specify gitlab url if applicable
+- Create `.env` file as documented below
 
 ### How to run
 
@@ -61,6 +59,20 @@ Access web locally:
 Check `Makefile` for shell commands if you want to run them with modified
 parameters.
 
+### Local .env file
+
+Local `.env` file is required to run the application, a basic example of such file contains the following:
+
+```
+ZOO_DEBUG=1
+ZOO_GITHUB_TOKEN=...
+ZOO_GITLAB_TOKEN=...
+ZOO_GITLAB_URL=https://gitlab.com
+```
+
+Version control tokens only need read access to repositories. 
+
+
 ## Testing
 
 Run all tests: `$ make test`