Added yaml tl;dr and yamllint notes to the kb

knowledge base/yamllint.md

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+# Yamllint
+
+A linter for YAML files written in Python and compatible with Python 3 only.
+
+## TL;DR
+
+```shell
+# Use a specific configuration file.
+yamllint -c /path/to/config file.yaml
+
+# Pass custom configuration options on the CLI.
+yamllint -d "{extends: relaxed, rules: {line-length: {max: 120}}}" file.yaml
+```
+
+## Configuration
+
+`yamllint` uses a set of [rules] to check YAML files for problems. Each rule is independent from the others, and can be enabled, disabled or tweaked. All these settings can be gathered in a configuration file.
+
+To use a custom configuration file, use the `-c` option:
+
+```shell
+yamllint -c /path/to/config file.yaml
+```
+
+If no such option is provided, `yamllint` will look for a configuration file in the following locations (by order of preference):
+
+- `.yamllint`, `.yamllint.yaml` or `.yamllint.yml` in the current working directory
+- the file referenced by `$YAMLLINT_CONFIG_FILE`, if set
+- `$XDG_CONFIG_HOME/yamllint/config`
+- `~/.config/yamllint/config`
+
+Finally, if no config file is found the default configuration is applied.
+
+You can avoid the need to redefine every rule when writing a custom configuration file `extend`ing the default one or any other already-existing configuration file:
+
+```yaml
+extends: default
+rules:
+  comments-indentation: disable   # don't bother me at all with this rule
+```
+
+```yaml
+extends: relaxed
+  line-length:   # just warn if a line is longer than 120 chars, instead of failing at 81
+    max: 120
+    level: warning
+  indentation:   # loosen up on block sequences indentation
+    indent-sequences: whatever
+```
+
+## Further readings
+
+- [GitHub] page
+- Yamllint's [documentation]
+- [Rules]
+
+[documentation]: https://yamllint.readthedocs.io/en/stable
+[github]: https://github.com/adrienverge/yamllint
+[rules]: https://yamllint.readthedocs.io/en/stable/rules.html