remove build dir in snippet and in our CI

Fixes #106 (closed)

examples/CI_code_snippets/3.ex_CI_upload_ossr.md

@@ -43,7 +43,6 @@ deploy_zenodo:
 
 ```
 
-
 ### Upload to Sandbox Zenodo
 ```yaml
 stages:
@@ -59,3 +58,11 @@ deploy_zenodo:
   only:
     - tags
 ```
+
+Note: you might want to restore the directory to its tag stage if you made changes in previous CI stages
+(for example removing build subdirs from previous test stages).
+You may do so using adding the following in the `before_script` section:
+```
+- apt-get install git -y
+- git reset --hard HEAD && git clean -fd
+```