Fix typo and add fix Markdown section

doc.zih.tu-dresden.de/CONTRIBUTE.md

@@ -33,7 +33,7 @@ docs/index.md:8:131 MD013/line-length Line length [Expected: 130; Actual: 138]
 
 configuration file: `.markdownlint.json`
 
-Before commiting, invoke the script `util/lint-changes.sh` which calls the markdownlint tool for all
+Before committing, invoke the script `util/lint-changes.sh` which calls the markdownlint tool for all
 (git-)changed markdown files
 
 ```shell
@@ -46,6 +46,13 @@ README.md:22 MD022/blanks-around-headings/blanks-around-headers Headings should
 [8< 8<]
 ```
 
+#### Fix Markdown
+
+The markdownlint-cli tool can also be used to fix markdown source file.
+```shell
+markdownlint --fix [--config .markdownlint.json] docs/index.md
+```
+
 ## Check Links
 
 We can use `util/check-links.sh` or [markdown-link-check](https://github.com/tcort/markdown-link-check)
@@ -99,4 +106,6 @@ drwxr-xr-x   3 zwulf p_zwulf      4096 Feb 12  2020 data
   * `[...]`
   * TODO: Choose one.
 
+### Code Blocks
 
+All code blocks should be runnable from a login node.