Update allocate-timeout.md

Author: rustatian

known-issues/allocate-timeout.md

@@ -2,8 +2,12 @@
 
 RoadRunner allocates workers like usual processes (via `fork` + `exec` syscalls). While RoadRunner is in the process of creating a worker (connecting to the pipes, TCP, etc.), some part of the worker might freeze the initial handshake. RoadRunner waits `pool.allocate_timeout` time for handshake to complete and return this error if `pool.allocate_timeout` exceeded.
 
-How to fix that?  
+## How to fix that?  
 
 1. Check the `pool.allocate_timeout` option. It should be in the form of `pool.allocate_timeout: 1s` or `pool.allocate_timeout: 1h`, so you should specify the units of measurement. Also, keep in mind, that `1s` for the allocate timeout might be a very small value, try to increase it.
 2. `xdebug` might freeze the worker spawn while improperly configured. See this tutorial: [link](../php/debugging.md)
 3. If you use a server's relay other than `pipes`, check [this options](https://github.com/roadrunner-server/roadrunner/blob/master/.rr.yaml#L75). It's responsible for the initial handshake timeout between RR and PHP process established via `sockets` or `TCP`.
+
+## What is `allocate_timeout` pool option?
+
+The `pool.allocate_timeout` is responsible for 2 things in RoadRunner: first - timeout to allocate a PHP worker when RoadRunner is starting up (initializing workers). Second - timeout to take the worker from the internal workers container, for example, when a request arrives.