Add rule to remove shell prompt literals $

Rule added to handle cases where the $ symbol is used in the command,
this usually happens when the command is copy pasted from a
documentation that includes the shell prompt symbol in the code blocks.

README.md

@@ -279,6 +279,7 @@ following rules are enabled by default:
 * `quotation_marks` – fixes uneven usage of `'` and `"` when containing args';
 * `path_from_history` – replaces not found path with similar absolute path from history;
 * `react_native_command_unrecognized` – fixes unrecognized `react-native` commands;
+* `remove_shell_prompt_literal` – remove leading shell prompt symbol `$`, common when copying commands from documentations;
 * `remove_trailing_cedilla` – remove trailling cedillas `ç`, a common typo for european keyboard layouts;
 * `rm_dir` – adds `-rf` when you try to remove a directory;
 * `scm_correction` – corrects wrong scm like `hg log` to `git log`;

tests/rules/test_remove_shell_prompt_literal.py

@@ -0,0 +1,32 @@
+import pytest
+from thefuck.rules.remove_shell_prompt_literal import match, get_new_command
+from thefuck.types import Command
+
+
+@pytest.mark.parametrize('command',
+    [
+        Command('$ cd newdir', '$: command not found'),
+        Command(' $ cd newdir', '$: command not found'),
+    ])
+def test_match(command):
+    assert match(command)
+
+
+@pytest.mark.parametrize('command',
+    [
+        Command('$', ''),
+        Command('$?', ''),
+        Command(' $?', ''),
+        Command('', ''),
+    ])
+def test_not_match(command):
+    assert not match(command)
+
+
+@pytest.mark.parametrize('command, new_command',
+    [
+        (Command('$ cd newdir', ''), 'cd newdir'),
+        (Command('$ python3 -m virtualenv env', ''), 'python3 -m virtualenv env'),
+    ])
+def test_get_new_command(command, new_command):
+    assert get_new_command(command) == new_command

thefuck/rules/remove_shell_prompt_literal.py

@@ -0,0 +1,20 @@
+"""Fixes error for commands containing the shell prompt symbol '$'.
+
+This usually happens when commands are copied from documentations
+including them in their code blocks.
+
+Example:
+> $ git clone https://github.com/nvbn/thefuck.git
+bash: $: command not found...
+"""
+
+import re
+
+def match(command):
+    return ("$: command not found" in command.output and
+            re.search(r"^[\s]*\$ [\S]+", command.script) is not None)
+
+def get_new_command(command):
+    return command.script.replace("$", "", 1).strip()
+
+requires_output = True