Markdown linter (#1309)

* Add markdown linting

- add linter default rules
- adapt rules to current code
- fix the code for linting to pass
- add CI check

fix #1243

* Fix markdown for Substrate
* Fix tooling install
* Fix workflow
* Add documentation
* Remove trailing spaces
* Update .github/.markdownlint.yaml

Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
* Fix mangled markdown/lists
* Fix captalization issues on known words

substrate/bin/utils/subkey/SECURITY.md

@@ -1,8 +1,9 @@
 # Keys and Security
 
-The following information is not exhaustive but meant to prevent the most common mistakes.
-You can read more about security and risks in the [Polkadot Wiki](https://wiki.polkadot.network/docs/learn-account-generation).
-The Polkadot network has a few **test networks**, e.g. **Westend**. Test networks are a great way to experiment and learn safely as you can lose tokens on those networks without any financial consequences.
+The following information is not exhaustive but meant to prevent the most common mistakes. You can read more about
+security and risks in the [Polkadot Wiki](https://wiki.polkadot.network/docs/learn-account-generation). The Polkadot
+network has a few **test networks**, e.g. **Westend**. Test networks are a great way to experiment and learn safely as
+you can lose tokens on those networks without any financial consequences.
 
 `subkey` generates and provides 2 pieces of **secret** information:
 - **secret phrase**: a bunch of words, exactly 12 by default (can be 12, 15, 18, 21 or 24)
@@ -10,16 +11,22 @@ The Polkadot network has a few **test networks**, e.g. **Westend**. Test network
 
 There are 2 risks related to private keys:
 - loss of keys: this can happen if you don't have a proper backup
-- leak of the keys: this can unfortunately happen in many ways, including malware, phishing, key logger, backups on system that are online and not properly secured
+- leak of the keys: this can unfortunately happen in many ways, including malware, phishing, key logger, backups on
+  system that are online and not properly secured
 
 You want to ensure that:
 - you **do not lose** those secrets
 - **no one but you can access** those secrets
 
-☠️ **DO NOT SHARE** your mnemonic phrase or secret seed with ANYONE under **ANY** circumstances. Doing so would give them access to your funds and to send transactions on your behalf.
+☠️ **DO NOT SHARE** your mnemonic phrase or secret seed with ANYONE under **ANY** circumstances. Doing so would give
+them access to your funds and to send transactions on your behalf.
 
-☠️ If someone is asking for your **secret** phrase or **secret** seed, you can be **SURE** they are attempting to steal your funds.
+☠️ If someone is asking for your **secret** phrase or **secret** seed, you can be **SURE** they are attempting to steal
+your funds.
 
-✅ It is however fine to share your **SS58 Address** as this is meant to be public information and is needed by anyone you want to be able to make transfer to or otherwise interact with your account. They will only ever need your **Public Address**.
+✅ It is however fine to share your **SS58 Address** as this is meant to be public information and is needed by anyone
+you want to be able to make transfer to or otherwise interact with your account. They will only ever need your **Public
+Address**.
 
-⚠️ While using the same key on multiple networks is possible, it is usually **not** recommended unless you have good motivations for doing so and understand the associated risks and drawbacks.
+⚠️ While using the same key on multiple networks is possible, it is usually **not** recommended unless you have good
+motivations for doing so and understand the associated risks and drawbacks.