Added - authorization instructions to ReadMe.md.

ReadMe.md

@@ -13,25 +13,49 @@ Therefore, it is not possible to install it through the marketplace
 
 Alternative installation:
 
-1. (Optional) Download a release version of the add-on
-2. Open Google Sheets
-3. Open Google Apps Scripts (located in the `Extensions` menu on the toolbar)
+1. Open Google Sheets
+2. Open Google Apps Scripts (located in the `Extensions` menu on the toolbar)
+3. (Optional) Download `Phonebook.gs` from one of the releases
 4. Copy the entire contents of `Phonebook.gs`
 5. Replace the `function myFunction()` in `Code.gs` with the contents of `Phonebook.gs`
 6. Reload Google Sheets (it might take more than one try)
 7. Done
 
-Note: The script will only work for the specific Google Sheet. You will have to repeat this process for different sheets.
+Note: The script will only work for the one specific Google Sheet. You will have to repeat this process for different sheets.
 
 ![Step 4](/resources/installation/step_4.png)
 ![Step 5-1](/resources/installation/step_5_1.png)
 ![Step 5-2](/resources/installation/step_5_2.png)
 ![Step 6](/resources/installation/step_6.png)
 
+## Authorization
+---
+The add-on is not a verified Google app.
+Google Sheets will ask for permissions to run the script on the attached Google Sheets document the first time you try to use the add-on.
+You will have to sign in with a Google account and give the add-on **permissions** to **see**, **edit**, **create**, **delete** Google Sheet documents.
+The add-on only **sees** (reads) and **edits** Google Sheet documents, but the permissions are grouped together.
+
+Authorization:
+
+1. Attempt to use the add-on (e.g. try to select a phonebook)
+2. Authorization Required - Google Sheets will ask for permission to run the script
+3. Sign in with a Google account
+4. Click `Advanced`
+5. Click `Go to Untitled project (unsafe)`
+6. Click `Allow`
+7. Done
+
+![Step 1](/resources/authorization/authorization_1.png)
+![Step 2](/resources/authorization/authorization_2.png)
+![Step 3](/resources/authorization/authorization_3.png)
+![Step 4](/resources/authorization/authorization_4.png)
+![Step 5](/resources/authorization/authorization_5.png)
+![Step 6](/resources/authorization/authorization_6.png)
+
 
 ## Usage
 ---
-In order to use this add-on you need to create a separate sheet containing pairs of phone numbers and names that will act as a 'phonebook'. This sheet will be used by the add-on as a reference to know which phone numbers need to be replaced in a subpoena. The pairs of `[Number, Name]` must be located in the first two columns of this sheet without any empty rows.
+In order to use this add-on you need to create a separate sheet containing pairs of phone numbers and names that will act as a 'phonebook'. This sheet will be used by the add-on as a reference to know which phone numbers need to be replaced in a subpoena. The pairs of `[Number, Name]` must be located in the **first two columns** of this sheet **without any empty rows**.
 
 ![Screenshot_1](/resources/screenshots/screenshot_1.png)