Added the contributing doc (#706)

CONTRIBUTING.md

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+Contributing to cloud-governance
+=====================
+
+## How to Contribute
+The cloud-governance project welcomes contributions from everyone!  Please read the below steps to see how you can contribute.
+
+## Environment Setup
+
+- Before going further we assume you must have the python3 installed in your system.
+
+- Clone `main` branch for latest, or a specific release branch
+
+```
+git clone --single-branch --branch main https://github.com/redhat-performance/cloud-governance.git
+```
+- Change directory to the code and create your own branch to work
+
+```
+cd cloud-governance/
+git checkout -b <name_of_change>
+python3.9 -m venv .venv
+source ./.venv/bin/activate
+pip install -r requirmenets.txt
+```
+
+## Adding the New Policies
+
+- Choose the policy type by cloud in [policy](cloud_governance/policy) folder.
+- Choose the policy type that need to be created. \
+If the policy is cleanup/ idle choose cleanup folder.
+- You will find the common methods that will be useful for tracking in [helper](cloud_governance/common/helpers) folder by cloud.
+
+### Policy Directory Structure
+
+- main
+  - aws_main_operations.py
+  - main.py
+- common
+  - helper
+    - aws
+      - aws_cleanup_operations.py
+    - azure
+      - azure_cleanup_operations.py
+    - cleanup_operations.py
+    - Json_datetime_encoder.py
+- policy
+  - aws
+      - cleanup
+        - ec2_run
+          - ebs_use
+        - tagging
+        - cost_reports
+  - policy_runners
+    - aws
+      - policy_runner.py
+      - upload_s3.py
+    - azure
+      - policy_runner.py
+    - elasticsearch
+      - upload_elasticsearch.py
+    - common
+      - abstract_policy_runner.py
+      - abstract_upload.py
+
+###  Rules to implement Policies
+
+- Each policy needs to be run in two modes dry_run=yes/ no.
+- RUN_ACTIVE_REGIONS=True env variable runs the policy in all active regions and the data will be uploaded to the ElasticSearch and s3/ storage bucket.
+  This is already implemented in [policy_runner](cloud_governance/policy/policy_runners/aws/policy_runner.py).
+- The S3 upload data format is key/region_name/policy/YYYY/MM/DD structure.
+- Each policy will have the option to skip the action by having the resource tag **Policy=notdelete** or **skip=not_delete**.
+- Each policy will have the env #DAYS_TO_TAKE_ACTION variable, which will take action that equals the days of DaysCount.
+- Each policy has the alert days, which will be #DAYS_TO_TAKE_ACTION - 4 and alert the user if we configured the policy alert. ( Note: Currently this is disabled due to that we have the aggregated message policy )
+- Possibilities for checking the dry_run days.
+  - If an instance is Using/ stopped then set DaysCount=0
+  - If an instance is running increment the counter based on dry_run=no mode by +1 else set 0
+  - If dry_run == "no":
+    - CountDays=date@#1
+  - else:
+    - If dry_run == "yes":
+      - CountDays=date@#0