update contrib guide

CONTRIBUTING.md

@@ -2,7 +2,7 @@
 ## Welcome :smile:
 ### To start contributing, follow these steps :point_down::
 
-1. [Star](https://help.github.com/en/articles/about-stars) :star: the repository.
+1. [Star](https://help.github.com/en/articles/about-stars) :star: the repository (not necessary but it helps maintainers).
 2. [Fork](https://help.github.com/en/articles/fork-a-repo) :fork_and_knife: it.
 3. Create [Branch](https://help.github.com/en/articles/about-branches) :herb: with your feature `<feature>`.
 4. [Push](https://help.github.com/en/articles/pushing-to-a-remote) changes.
@@ -14,11 +14,13 @@
    - [map](https://github.com/Bhupesh-V/30-seconds-of-cpp/tree/master/map)
    - [vector](https://github.com/Bhupesh-V/30-seconds-of-cpp/tree/master/vector)
    - [queue](https://github.com/Bhupesh-V/30-seconds-of-cpp/tree/master/queue)
+   - [priority_queue](https://github.com/Bhupesh-V/30-seconds-of-cpp/tree/master/priority_queue)
+   - [unordered_map](https://github.com/Bhupesh-V/30-seconds-of-cpp/tree/master/unordered_map)
 7. If you are feeling confused on what to contribute, head over to [Projects](https://github.com/Bhupesh-V/30-seconds-of-cpp/projects), select the directory you want to contribute to for e.g choose `<algorithm>` & from the **Algorithms To Implement** column select any one method.You can either submit a small C++ code snippet demonstrating the same in the `snippets` directory or submit a overview of the choosen method in `<name_of_directory>` see for example [all_of.md](https://github.com/Bhupesh-V/30-seconds-of-cpp/blob/master/algorithm/all_of.md).
-8. Always follow the style guide(see below).
-9. Do not update any `README` or `todo.txt` files (unless you find a typo :sweat_smile:)
-9. Enjoy contributing :yum:.
-10. If you have any doubts, open an [issue](https://github.com/Bhupesh-V/30-seconds-of-cpp/issues/new). 
+8. Always follow the [style guide](https://github.com/Bhupesh-V/30-seconds-of-cpp/blob/master/CONTRIBUTING.md#style-guide).
+9. Do not update any `README.md` or `todo.txt` files (unless you find a typo 😅)
+10. Enjoy contributing!.
+11. If you have any doubts, open an [issue](https://github.com/Bhupesh-V/30-seconds-of-cpp/issues/new). 
 
 For adding functions in different directories, use the following template (copy from raw format): 
 
@@ -45,6 +47,7 @@ For adding functions in different directories, use the following template (copy
 ---
 
 # Style Guide
+
 Follow this style guide to add sample programs:
 
 1. Naming Style: 
@@ -81,7 +84,7 @@ Follow this style guide to add sample programs:
 5. Add appropriate comments wherever necessary to explain the code.
 > Programs wth NO Comments at all will not be merged.
 
-6. Expression should be readable, Use 1 space between different TOKENS.
+6. Expression should be readable, Use 1 space between different tokens.
 ```cpp 
     galaxy=stars+asteroids          // ❌
     galaxy = stars + asteroids      // ✅.
@@ -93,14 +96,14 @@ Follow this style guide to add sample programs:
         std::cout << i << " ";               // ❌
 
     for (int i = 0;i < 45; ++i){
-        std::cout << i <<" ";               // ✅.
+        std::cout << i << " ";               // ✅.
     }
 ```
-8. Always use pre-increment(++i) while looping instead of post-increment(i++).
+8. Always use pre-increment(++i) in loops instead of post-increment(i++).
 
 9. When submitting `markdown` files of methods in different directories, name your file exactly as the function/method name. For example `push_back.md`, `swap.md` etc.
 
-10. Always use prefix ```std::``` for functions and types from the std namespace, either on the `markdown` files and on the snippets files.
+10. Always use prefix ```std::``` for functions and types from the std namespace, either on the `markdown` files or on the snippet code files.
 ```cpp 
     using namespace std;   // ❌ 
     vector<int> ...;       // ❌