H6: Update table of contents

exercises/h6.md

@@ -9,7 +9,7 @@ This exercise is a part of [Linux servers (ICT4TN021, spring 2018) // Linux-palv
 *Table of contents:*
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-- [a) Write and execute "Hello world" in three code languages of your choice. Set up a necessary development environments.](https://github.com/Fincer/linux_server_setup/blob/master/exercises/h6.md#a-write-and-execute-hello-world-in-three-code-languages-of-your-choice-set-up-a-necessary-development-environments)
+- [a) **Hello World** Write and execute "Hello world" in three code languages of your choice. Set up a necessary development environments.](https://github.com/Fincer/linux_server_setup/blob/master/exercises/h6.md#a-write-and-execute-hello-world-in-three-code-languages-of-your-choice-set-up-a-necessary-development-environments)
 
     - [Perl (hello.pl)](https://github.com/Fincer/linux_server_setup/blob/master/exercises/h6.md#perl-hellopl)
 
@@ -17,7 +17,7 @@ This exercise is a part of [Linux servers (ICT4TN021, spring 2018) // Linux-palv
 
     - [C (hello.c)](https://github.com/Fincer/linux_server_setup/blob/master/exercises/h6.md#c-helloc)
 
-- [b) (optional) Write a simple program for some practical purpose with each language. Ideas: utilize the key benefits of your language of choice. Take an input value from a user, generate a calculation and print the output (input-processing-layout).](https://github.com/Fincer/linux_server_setup/blob/master/exercises/h6.md#b-optional-write-a-simple-program-for-some-practical-purpose-with-each-language-ideas-utilize-the-key-benefits-of-your-language-of-choice-take-an-input-value-from-a-user-generate-a-calculation-and-print-the-output-input-processing-layout)
+- [b) **Custom program** (optional) Write a simple program for some practical purpose with each language. Ideas: utilize the key benefits of your language of choice. Take an input value from a user, generate a calculation and print the output (input-processing-layout).](https://github.com/Fincer/linux_server_setup/blob/master/exercises/h6.md#b-optional-write-a-simple-program-for-some-practical-purpose-with-each-language-ideas-utilize-the-key-benefits-of-your-language-of-choice-take-an-input-value-from-a-user-generate-a-calculation-and-print-the-output-input-processing-layout)
 
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