doc: added the zstd_static descriptions

Author: tokers

README.md

@@ -8,14 +8,18 @@ zstd-nginx-module - Nginx module for the [Zstandard compression](https://faceboo
 * [Synopsis](#synopsis)
 * [Installation](#installation)
 * [Directives](#directives)
-  * [zstd_dict_file](#zstd_dict_file)
-  * [zstd](#zstd)
-  * [zstd_comp_level](#zstd_comp_level)
-  * [zstd_min_length](#zstd_min_length)
-  * [zstd_types](#zstd_types)
-  * [zstd_buffers](#zstd_buffers)
+  * [ngx_http_zstd_filter_module](#ngx_http_zstd_filter_module)
+    * [zstd_dict_file](#zstd_dict_file)
+    * [zstd](#zstd)
+    * [zstd_comp_level](#zstd_comp_level)
+    * [zstd_min_length](#zstd_min_length)
+    * [zstd_types](#zstd_types)
+    * [zstd_buffers](#zstd_buffers)
+  * [ngx_http_zstd_static_module](#ngx_http_zstd_static_module)
+    * [zstd_static](#zstd_static)
 * [Variables](#variables)
-  * [$zstd_ratio](#$zstd_ratio)
+  * [ngx_http_zstd_filter_module](#ngx_http_zstd_filter_module)
+    * [$zstd_ratio](#$zstd_ratio)
 * [Author](#author)
 
 # Status
@@ -42,69 +46,101 @@ server {
         proxy_pass http://foo.com;
     }
 }
+
+server {
+    listen 127.0.0.1:8081;
+    server_name localhost;
+
+    location / {
+        zstd_static on;
+        root html;
+    }
+}
 ```
 
 # Installation
 
-To use this module, configure your nginx branch with `--add-module=/path/to/zstd-nginx-module`. Several points should be taken care.
+To use theses modules, configure your nginx branch with `--add-module=/path/to/zstd-nginx-module`. Several points should be taken care.
 
 * You can set environment variables `ZSTD_INC` and `ZSTD_LIB` to specify the path to `zstd.h` and the path to zstd shared library represently.
 * static library will be tried prior to dynamic library, since this Nginx module uses some **advanced APIs** where static linking is recommended.
 * System's zstd bundle will be linked if `ZSTD_INC` and `ZSTD_LIB` are not specified.
+* Both `ngx_http_zstd_static_module` and `ngx_http_zstd_filter_module` will be configured.
 
 # Directives
 
-## zstd_dict_file
+## ngx_http_zstd_filter_module
+
+The `ngx_http_zstd_filter_module` module is a filter that compresses responses using the "zstd" method. This often helps to reduce the size of transmitted data by half or even more.
+
+### zstd_dict_file
 
 **Syntax:** *zstd_dict_file /path/to/dict;*  
 **Default:** *-*  
 **Context:** *http*  
 
 Specifies the external dictionary.
 
-## zstd
+### zstd
 
 **Syntax:** *zstd on | off;*  
 **Default:** *zstd off;*  
 **Context:** *http, server, location, if in location*
 
 Enables or disables zstd compression for response.
 
-## zstd_comp_level
+### zstd_comp_level
 
 **Syntax:** *zstd_comp_level level;*  
 **Default:** *zstd_comp_level 1;*  
 **Context:** *http, server, location*
 
 Sets a zstd compression level of a response. Acceptable values are in the range from 1 to `ZSTD_maxCLevel()`.
 
-## zstd_min_length
+### zstd_min_length
 
 **Syntax:** *zstd_min_length length;*  
 **Default:** *zstd_min_length 20;*  
 **Context:** *http, server, location*
 
 Sets the minimum length of a response that will be compressed by zstd. The length is determined only from the "Content-Length" response header field.
 
-## zstd_types
+### zstd_types
 
 **Syntax:** *zstd_types mime-type ...;*  
 **Default:** *zstd_types text/html;*  
 **Context:** *http, server, location*
 
 Enables ztd of responses for the specified MIME types in addition to "text/html". The special value "*" matches any MIME type.
 
-## zstd_buffers
+### zstd_buffers
 
 **Syntax:** *zstd_buffers number size;*  
 **Default:** *zstd_buffers 32 4k | 16 8k;*  
 **Context:** *http, server, location*
 
 Sets the number and size of buffers used to compress a response. By default, the buffer size is equal to one memory page. This is either 4K or 8K, depending on a platform.
 
+## ngx_http_zstd_static_module
+
+The `ngx_http_zstd_static_module` module allows sending precompressed files with the ".zst" filename extension instead of regular files.
+
+### zstd_static
+
+**Syntax:**	*zstd_static on | off | always;*
+**Default:** *gzip_static off;*
+**Context:** *http, server, location*
+
+Enables ("on") or disables ("off") checking the existence of precompressed files. The following directives are also taken into account: gzip_vary.
+
+With the "always" value, "zsted" file is used in all cases, without checking if the client supports it.
+
+
 # Variables
 
-## $zstd_ratio
+## ngx_http_zstd_filter_module
+
+### $zstd_ratio
 
 Achieved compression ratio, computed as the ratio between the original and compressed response sizes.