test: document POST /user/resend_email API testing (#897)

Fixes #875

docs/manual_tests/test_resend_email.md

@@ -0,0 +1,34 @@
+* Test 1 : Email is sent to registered user's email.
+
+     _Screenshot_: 
+
+     ![test_1](https://user-images.githubusercontent.com/42766576/94338862-3f38d580-0013-11eb-8638-4ed46f4e9e13.png)
+
+
+     _Expected Result_: SUCCESS (message: Check your email, a new verification email was sent.)
+
+     _Actual Result_: SUCCESS (message: Check your email, a new verification email was sent.)
+
+
+* Test 2:  Email is sent to the user who already confirmed their mail
+
+     _Screenshot_: 
+
+     ![test_2](https://user-images.githubusercontent.com/42766576/94338870-57a8f000-0013-11eb-8e83-1f1740242067.png)
+
+
+     _Expected Result_:  FAILURE (message: You already confirm your email)
+
+     _Actual Result_: FAILURE (message: You already confirm your email)
+
+
+* Test 3:  Email is sent to an email that is not registered in the system
+
+     _Screenshot_: 
+
+    ![test_3](https://user-images.githubusercontent.com/42766576/94338843-14e71800-0013-11eb-9993-560d36527534.png)
+
+
+     _Expected Result_:  FAILURE (message: You are not registered in the system.)
+
+     _Actual Result_: FAILURE (message: You are not registered in the system.)