Add contribution guidelines (#114)

* [#107] Add contribution guidelines

* [#107] Add link to bug bounty program, update coverage expectation in contribution guidelines

* [#107] Create pull_request_template.md

* [#107] Create issue_template.md

* Update pull_request_template.md

.github/issue_template.md

@@ -0,0 +1,18 @@
+**Description**
+
+...
+
+_Remove below if not relevant_
+
+**Steps to reproduce bug**
+- Step 1
+- Step 2
+- ...
+
+**Expected behaviour**
+
+...
+
+**Possible solutions with alternatives**
+
+...

.github/pull_request_template.md

@@ -0,0 +1,12 @@
+
+_Use one of the below_
+
+Fixes to #issue-number
+
+Relates to #issue-number
+
+**Changes in PR:**
+
+- Change 1
+- Change 2
+- ...

CONTRIBUTING.md

@@ -0,0 +1,43 @@
+# Contributing to Safe Core Protocol
+
+Even if you don't write code, there are many ways you can help improve the project.
+
+Here are some important resources:
+
+  * [Safe docs](https://docs.safe.global) tells you about Safe
+  * [Safe{Core} Protocol Specification](https://github.com/safe-global/safe-core-protocol-specs) tells you about the protocol specifications.
+
+## Submitting issues
+
+If you are submitting a feature request, please:
+
+  * Explain in detail the purpose and how it should work.
+  * Examples of how it should be implemented along with alternatives are welcome.
+
+If you are submitting a bug report, please:
+  * Refer to [Bug bounty program](https://docs.safe.global/safe-smart-account/security/bug-bounty-program) before creating submitting issue.
+  * Include the steps to reproduce the bug.
+  * Include the expected behavior.
+  * Possible solutions to fix the bug are welcome.
+
+## Submitting changes
+
+Please send a [GitHub Pull Request to safe-core-protocol repository](https://github.com/safe-global/safe-core-protocol) with a clear description of the proposed changes. Each pull request should be associated with an issue and should be made against the `main` branch.
+
+Branch naming convention:
+
+- For a new feature, use `feature-<issue-number>-short-description`
+- For a bug fix, use `fix-<issue-number>-short-description`
+
+Always write a clear log message for your commits. The commit message should look like this:
+
+    $ git commit -m "[#<issue-number>] A brief summary of the commit"
+
+Steps to be taken before submitting a pull request to be considered for review:
+- Documentation reflects the changes
+- Make sure test coverage is close to 100%
+- Make sure all tests are passing
+- Make sure there are no linting errors
+
+Thanks,
+Safe team