Added modes for file handling in index.md (#21902)

Added different modes that can be used and their description under "The Real Deal" Section.

guide/english/c/file-handling/index.md

@@ -168,6 +168,32 @@ The above methods only worked for the most basic of cases.  If you wanted to do
 To accomplish this, you will use a function called `fopen`.  This function takes two string parameters, the first being the file name and the second being the mode.
 Mode is basically permissions, so `r` for read, `w` for write, `a` for append.  You can also combine them, so `rw` would mean you could read and write to the file.  There are more modes, but these are the most used.
 
+There are a number of modes that can be used for file handling.
+
+**"r"**   **-**   **Open file for reading**
+
+**rb**   **-**   **Open file for reading in binary mode**
+
+**w**   **-**   **Open file for writing**
+
+**wb**   **-**   **Open file for writing in binary mode**
+
+**a**   **-**   **Open file for appending**
+
+**ab**   **-**   **Open file for appending in binary mode**
+
+**r+**   **-**   **Open file for both reading and writing**
+
+**rb+**   **-**   **Open file for both reading and writing in binary mode**
+
+**w+**   **-**   **Open file for both writing and reading**
+
+**wb+**   **-**   **Open file for both writing and reading in binary mode**
+
+**a+**   **-**   **Open file for both reading and appending**
+
+**ab+**   **-**   **Open file for both reading and appending in binary mode**
+
 After you have a `FILE` pointer, you can use basically the same IO commands you would've used, except that you have to prefix them with `f` and the first argument will be the file pointer.
 For example, `printf`'s file version is `fprintf`.