Revert "Since the git clone code is more efficient now we do not need this warning anymore."

This reverts commit a757c4a2.

While it is true that Grack memory use while sending data to a client
was improved, this does not change the fact that the Git processes
running on a GitLab server will use more memory for large repositories.

doc/install/requirements.md

@@ -55,7 +55,7 @@ it might require some work since GitLab uses several Gems that have native exten
 - 512MB is too little memory, GitLab will be very slow and you will need 250MB of swap
 - 768MB is the minimal memory size but we advise against this
-- 1GB supports up to 100 users
+- 1GB supports up to 100 users if you do not have individual repo's over 250MB
 - **2GB** is the **recommended** memory size and supports up to 1,000 users
 - 4GB supports up to 10,000 users