Merge branch 'clone-explanation' into 'master'

Explain where the memory recommendation comes from

The 250MB repo limit is caused by the git command line.

Also see MR !422

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 if you do not have individual repo's over 250MB
+- 1GB supports up to 100 users (with individual repositories under 250MB, otherwise git memory usage necessitates using swap space)
 - **2GB** is the **recommended** memory size and supports up to 1,000 users
 - 4GB supports up to 10,000 users