contributing.md file including the contribution instructions

CONTRIBUTING.md

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+# Contributing to SPDX Cryptographic Algorithm List
+
+* General technical questions or issues about the List can be sent to the SPDX technical team mailing list.
+* Questions or issues on any algorithm content can be reported through a [GitHub issue](https://github.com/spdx/cryptographic-algorithm-list/issues):
+   * Review first that your question or issue has not been reported already. If it has been, simple add a comment in the corresponding issue
+   * If there is no past record of your question or issue, please create a new issue
+* You are welcome to participate in any of the SPDX Cryptography Group weekly meetings. Check the [SPDX meetings list](https://github.com/spdx/meetings?tab=readme-ov-file#cryptography) to find out the schedule and connection details
+   * The agenda for the next meeting can be found in [this folder](https://hackmd.io/folders/oLPOEiStpNeFUH87rwJkm?nav=overview) while the approved minutes are merged into the [cryptography meeting folder](https://github.com/spdx/meetings/tree/main/cryptography) in bulks
+
+## Algorithm example
+
+This is an example of how an algorithm from the SPDX Cryptographic Algorithm List is described. This example correspond to no real algorithm.
+
+---
+```
+# SPDX-License-Identifier: CC0-1.0
+id: scale
+oid: 1.5.21.171.3.6.8
+name: SPDX Cryptographic Algorithm List Example
+cryptoClass: Symmetric-Key-Algorithm/Encoding
+commonkeySize: ['256', '512']
+specifiedkeySize: {min: '128', max: '256'}
+```
+---
+
+* All the properties are described on the SPDX Cryptographic Algorithms List [properties description file](https://github.com/spdx/cryptographic-algorithm-list/blob/main/crypto-algorithms-list-properties-description.md).
+* All the algorithms from the SPDX Cryptographic Algorithm List are included in the [yaml folder](https://github.com/spdx/cryptographic-algorithm-list/tree/main/yaml).
+   * For each algorithm you will find a .yaml file, with the name <id>.yaml , where <id> is the SPDX identifier for the corresponding cryptographic algorithm