docs(changelog): update information about using changelog command

Author: woile

docs/changelog.md

@@ -4,7 +4,28 @@ This command will generate a changelog following the commiting rules established
 
 ## Usage
 
-In the command line run
+```bash
+$ cz changelog --help
+usage: cz changelog [-h] [--dry-run] [--file-name FILE_NAME]
+                    [--unreleased-version UNRELEASED_VERSION] [--incremental]
+                    [--start-rev START_REV]
+
+optional arguments:
+  -h, --help            show this help message and exit
+  --dry-run             show changelog to stdout
+  --file-name FILE_NAME
+                        file name of changelog (default: 'CHANGELOG.md')
+  --unreleased-version UNRELEASED_VERSION
+                        set the value for the new version (use the tag value),
+                        instead of using unreleased
+  --incremental         generates changelog from last created version, useful
+                        if the changelog has been manually modified
+  --start-rev START_REV
+                        start rev of the changelog.If not set, it will
+                        generate changelog from the start
+```
+
+### Examples
 
 ```bash
 cz changelog
@@ -14,15 +35,9 @@ cz changelog
 cz ch
 ```
 
-It has support for incremental changelog:
-
-- Build from latest version found in changelog, this is useful if you have a different changelog and want to use chommitizen
-- Update unreleased area
-- Allows users to manually touch the changelog without being rewritten.
-
 ## Constrains
 
-At the moment this features is constrained only to markdown files.
+changelog generation is constrained only to **markdown** files.
 
 ## Description
 
@@ -55,6 +70,60 @@ and the following variables are expected:
 
 - **required**: is the only one required to be parsed by the regex
 
+## Configuration
+
+### `unreleased_version`
+
+There is usually an egg and chicken situation when automatically
+bumping the version and creating the changelog.
+If you bump the version first, you have no changelog, you have to
+create it later, and it won't be included in
+the release of the created version.
+
+If you create the changelog before bumping the version, then you
+usually don't have the latest tag, and the _Unreleased_ title appears.
+
+By introducing `unreleased_version` you can prevent this situation.
+
+Before bumping you can run:
+
+```bash
+cz changelog --unreleased_version="v1.0.0"
+```
+
+Remember to use the tag instead of the raw version number
+
+For example if the format of your tag includes a `v` (`v1.0.0`), then you should use that,
+if your tag is the same as the raw version, then ignore this.
+
+Alternatively you can directly bump the version and create the changelog by doing
+
+```bash
+cz bump --changelog
+```
+
+### `file-name`
+
+This value can be updated in the `toml` file with the key `changelog_file` under `tools.commitizen`
+
+Specify the name of the output file, remember that changelog only works with markdown.
+
+```bash
+cz changelog --file-name="CHANGES.md"
+```
+
+### `incremental`
+
+Benefits:
+
+- Build from latest version found in changelog, this is useful if you have a different changelog and want to use commitizen
+- Update unreleased area
+- Allows users to manually touch the changelog without being rewritten.
+
+```bash
+cz changelog --incremental
+```
+
 ## TODO
 
 - [ ] support for hooks: this would allow introduction of custom information in the commiter, like a github or jira url. Eventually we could build a `CzConventionalGithub`, which would add links to commits