add a document (stub) for common problems

fixes #29

doc/TOC.md

@@ -6,6 +6,7 @@
 
 * [Usage](usage.md) — Overview of the project contents.
 * [Nginx.conf](nginx-conf.md) —General introduction to the main config file.
+* [Common problems](common-problems.md) —Dealing with commonly-encounterederrors.
 
 ## Related projects
 

doc/common-problems.md

@@ -0,0 +1,22 @@
+[Nginx Server Configs homepage](https://github.com/h5bp/server-configs-nginx)
+ | [Documentation table of contents](TOC.md)
+
+# Common Problems
+
+## types_hash errors
+
+Depending on the server architecture, it's possible to get the following error:
+
+> could not build the types_hash, you should increase either
+> types_hash_max_size: 1024 or types_hash_bucket_size: 32
+
+Nginx uses [hash tables](http://nginx.org/en/docs/hash.html) to speed up certain
+tasks, usually the default value is sufficient but depending on the actual server
+config this error might be encountered. The solution is to do exactly what the
+error message suggests, but adding to nginx.conf the following:
+
+    # add this to the http context
+    types_hash_max_size: 1024;
+
+    ## OR add this to the http context, don't need both
+    # types_hash_bucket_size: 32