Added antigen notes to the knowledge base

knowledge base/antigen.md

@@ -0,0 +1,27 @@
+# Antigen
+
+## Troubleshooting
+
+### While loading, a completion fails with error `No such file or directory`.
+
+Example:
+
+```shell
+tee: /Users/user/.antigen/bundles/robbyrussell/oh-my-zsh/cache//completions/_helm: No such file or directory
+/Users/user/.antigen/bundles/robbyrussell/oh-my-zsh/plugins/helm/helm.plugin.zsh:source:9: no such file or directory: /Users/user/.antigen/bundles/robbyrussell/oh-my-zsh/cache//completions/_helm
+```
+
+The issue is due of the `$ZSH_CACHE_DIR/completions` being missing and `tee` not creating it on Mac OS X. Create the missing `completions` directory and re-run antigen:
+
+```shell
+mkdir -p $ZSH_CACHE_DIR/completions
+antigen apply
+```
+
+## Further readings
+
+- [Github]'s repository
+- Antigen's [Wiki]
+
+[github]: https://github.com/zsh-users/antigen
+[wiki]: https://github.com/zsh-users/antigen/wiki