Update README.md

Author: DosX-dev

README.md

@@ -4,6 +4,20 @@ This program is designed to determine the file type using signatures according t
 ## About
 This console program takes an argument `--file` which specifies the path to the file that needs to be examined. The output will contain the resulting format, description and some technical data (for example, the presence of compressed entropy data)
 
+## Database rules format
+```
+{STRING_NAME}|{STRING_FILE_TYPE}|{STRING_DESCRIPTION}|{MASK_SIGNATURE}
+```
+ * Use ".."/"??" to indicate an unknown byte (like "0000..29..11...00")
+ * Use the ' character to wrap an ASCII string (like "000000'String in the file!'000029")
+
+The signature is read only from the beginning of the file.
+
+Example of rule:
+```
+Lua Bytecode|Script|Lua machine code|1B'Lua'..00
+```
+
 ## Run on Linux
 Use the `mono-complete` package to use the program on Linux:
 ```