feat: Update closed contribution documentation with new branch (#330)

Thanks to some follow up work by @eepifanova, we can now target the main
branch for closed content work. This commit updates the documentation to
reference the main branch, and also adds specificity of origin and
remote when referencing it for clarity.

It also adds missing punctuation, and adjusts spacing in an early
paragraph using a line break.

Author: ADubhlaoich

CLOSED_CONTRIBUTIONS.md

@@ -7,7 +7,9 @@ Sensitive content might include:
 - Security content, including personally identifying information (PII).
 - Content / features that are not yet ready to be announced.
 
-We work in public by default, so this process should only be used on a case by case basis by F5 employees. For standard content releases, review the [Contributing guidelines](/CONTRIBUTING.md)
+We work in public by default, so this process should only be used on a case by case basis by F5 employees. 
+
+For standard content releases, review the [Contributing guidelines](/CONTRIBUTING.md).
 
 ## Overview
 
@@ -34,10 +36,10 @@ git remote add internal [email protected]:<closed-url>.git
 git fetch
 ```
 
-Check out the `documentation` branch, and use it to create a feature branch. **Ensure that you prefix all branch names with `internal/`**
+Check out the remote `main` branch, and use it to create a feature branch. **Ensure that you prefix all branch names with `internal/`**
 
 ```shell
-git checkout internal/documentation
+git checkout internal/main
 git checkout -b internal/feature
 ```
 
@@ -53,7 +55,7 @@ Open a pull request when you are ready to receive feedback from stakeholders.
 
 After any iterative work, close the pull request. Since the closed repository is a mirror of the open one, we do not merge changes to it.
 
-Change back to `main`, create a new branch, merge your internal branch and push to origin.
+Change back to the origin `main` branch, create a new branch, merge your internal branch and push to origin.
 
 ```shell
 git checkout main