Add description for whatis command (#31)

* Add whatis command

* Edit mistype

README.md

@@ -38,7 +38,18 @@ $ echo $AWS_HOME
 /Users/adnanadnan/.aws
 ```
 
-### b. `whereis`
+### b. `whatis`
+whatis shows description for user commands, system calls, library functions, and others in manual pages
+```bash
+whatis something
+```
+Example:
+```bash
+$ whatis bash
+bash (1)             - GNU Bourne-Again SHell
+```
+
+### c. `whereis`
 whereis searches for executables, source files, and manual pages using a database built by system automatically.
 ```bash
 whereis name
@@ -49,7 +60,7 @@ $ whereis php
 /usr/bin/php
 ```
 
-### c. `which`
+### d. `which`
 which searches for executables in the directories specified by the environment variable PATH. This command will print the full path of the executable(s).
 ```bash
 which program_name 
@@ -60,7 +71,7 @@ $ which php
 /c/xampp/php/php
 ```
 
-### d. clear
+### e. clear
 Clears content on window.
 
 ## 1.1. File Operations