Rephrase few parts from contributing doc

See: rspec/rspec-core#2813

Author: benoittgt

common_plaintext_files/CONTRIBUTING.md.erb

@@ -71,11 +71,11 @@ In general the process is:
 2. Pin the repositories to each other.
 3. Check they pass (go green).
 4. Await review if appropriate.
-5. Remove the commit from one. We will merge ignoring the failure.
-6. Remove the commit from the other, check it passes with the other commit now on main.
+5. Remove the commit from step 2. We will merge ignoring the failure.
+6. Remove the commit from the other, check it passes with the other commit now on `main`.
 7. Merge the other.
-8. Rebuild the other main to check it still passes.
+8. We will trigger builds for the `main` branch of affected repositories to check if everything is in order.
 
-Steps 5-8 should happen contiguously (e.g. one after another but within a short timespan)
+Steps 5-8 should happen continuously (e.g. one after another but within a short timespan)
 so that we don't leave a broken main around. It is important to triage that build process
 and revert if necessary.