Update readme (#2)

* add check for custom exceptions
* add integration test for suppressing
* add check for re-raised exceptions
* add guide for fixing the linting problems

README.md

@@ -1,2 +1,193 @@
 # flake8-error-link
-A linter that ensures all raised Exceptions include an error with a link to more information
+
+Have you ever encountered an error when using a package and then gone to Google
+to find out how to solve the error? Wouldn't your users prefer to go directly
+to your documentation that tells them exactly what went wrong and how to
+resolve that error? `flake8-error-link` checks the way exceptions are raised in
+your code base to ensure that a link with more information is provided.
+
+## Getting Started
+
+```shell
+python -m venv venv
+source ./venv/bin/activate
+pip install flake8 flake8-error-link
+flake8 source.py
+```
+
+On the following code:
+
+```Python
+# source.py
+raise Exception
+```
+
+This will produce warnings such as:
+
+```shell
+source.py:1:0: ELI001 builtin exceptions should be raised with a link to more information: https://github.com/jdkandersson/flake8-error-link#fix-eli001
+```
+
+This can be resolved by changing the code to:
+
+```Python
+# source.py
+raise Exception("more information: https://github.com/jdkandersson/flake8-error-link#fix-eli001")
+```
+
+## Configuration
+
+The plugin adds the following configurations to `flake8`:
+
+* `--error-link-regex`: The regular expression to use to verify the way
+  exceptions are reased, defaults to
+  `more information: (mailto\:|(news|(ht|f)tp(s?))\:\/\/){1}\S+`
+
+
+## Rules
+
+A few rules have been defined to allow for selective suppression:
+
+* `ELI001`: checks that any builtin exceptions that are raised with constant
+   arguments include a link to more information.
+* `ELI002`: checks that any custom exceptions that are raised with constant
+   arguments include a link to more information.
+* `ELI003`: checks that any exceptions that are raised with variable arguments
+  include a constant argument with a link to more information.
+* `ELI004`: checks that any exceptions that are re-raised include a constant
+  argument with a link to more information.
+
+### Fix ELI001
+
+This linting rule is trigger by raising an inbuilt exception without providing
+a constant that includes a link to more information as one of the arguments to
+the constructor. For example:
+
+```Python
+raise Exception
+
+raise ValueError
+
+raise Exception()
+
+raise Exception("oh no! :(")
+```
+
+These examples can be fixed by using something like:
+
+```Python
+raise Exception(
+    "more information: https://github.com/jdkandersson/flake8-error-link#fix-eli001"
+)
+
+raise ValueError(
+    "more information: https://github.com/jdkandersson/flake8-error-link#fix-eli001"
+)
+
+raise Exception(
+    "more information: https://github.com/jdkandersson/flake8-error-link#fix-eli001"
+)
+
+raise Exception(
+    "oh no! :(",
+    "more information: https://github.com/jdkandersson/flake8-error-link#fix-eli001",
+)
+```
+
+### Fix ELI002
+
+This linting rule is trigger by raising a custom exception without providing
+a constant that include a link to more information as one of the arguments to
+the constructor. For example:
+
+```Python
+class CustomError(Exception):
+    pass
+
+raise CustomError
+
+raise CustomError()
+
+raise CustomError("bummer...")
+```
+
+These examples can be fixed by using something like:
+
+```Python
+class CustomError(Exception):
+    pass
+
+raise CustomError(
+    "more information: https://github.com/jdkandersson/flake8-error-link#fix-eli002"
+)
+
+raise CustomError(
+    "more information: https://github.com/jdkandersson/flake8-error-link#fix-eli002"
+)
+
+raise CustomError(
+    "bummer...",
+    "more information: https://github.com/jdkandersson/flake8-error-link#fix-eli002",
+)
+```
+
+### Fix ELI003
+
+This linting rule is trigger by raising an exception and passing at least one
+argument without providing a constant that include a link to more information
+as one of the arguments to the constructor. For example:
+
+```Python
+message = "gotcha"
+
+def get_message():
+    return message
+
+raise Exception(get_message())
+
+raise Exception(f"{message} quite badly")
+```
+
+These examples can be fixed by using something like:
+
+```Python
+message = "gotcha"
+
+def get_message():
+    return message
+
+raise Exception(
+    get_message(),
+    "more information: https://github.com/jdkandersson/flake8-error-link#fix-eli003",
+)
+
+raise Exception(
+    f"{message} quite badly, more information: https://github.com/jdkandersson/flake8-error-link#fix-eli003"
+)
+```
+
+### Fix ELI004
+
+This linting rule is trigger by re-raising an exception. For example:
+
+```Python
+try:
+    raise Exception(
+        "more information: https://github.com/jdkandersson/flake8-error-link#fix-eli004"
+    )
+except Exception:
+    raise
+```
+
+This example can be fixed by using something like:
+
+```Python
+try:
+    raise Exception(
+        "more information: https://github.com/jdkandersson/flake8-error-link#fix-eli004"
+    )
+except Exception as exc:
+    raise Exception(
+        "more information: https://github.com/jdkandersson/flake8-error-link#fix-eli004"
+    ) from exc
+```