Rules: git remote add instead of set-url if remote does not exist

Tests: Added test for git_remote_seturl_add

Rules: renamed new rule with a more appropriate name

README: added new rule

Style: Formatting

New rule: corrected test name

Developed tests

tests/rules/test_git_remote_seturl_add.py

@@ -0,0 +1,26 @@
+import pytest
+from thefuck.rules.git_remote_seturl_add import match, get_new_command
+from tests.utils import Command
+
+
+@pytest.mark.parametrize('command', [
+    Command(script='git remote set-url origin url', stderr="fatal: No such remote")])
+def test_match(command):
+    assert match(command)
+
+
+@pytest.mark.parametrize('command', [
+    Command('git remote set-url origin url', stderr=""),
+    Command('git remote add origin url'),
+    Command('git remote remove origin'),
+    Command('git remote prune origin'),
+    Command('git remote set-branches origin branch')
+    ])
+def test_not_match(command):
+    assert not match(command)
+
+@pytest.mark.parametrize('command, new_command', [
+    (Command('git remote set-url origin git@github.com:nvbn/thefuck.git'),
+     'git remote add origin git@github.com:nvbn/thefuck.git')])
+def test_get_new_command(command, new_command):
+    assert get_new_command(command) == new_command