add doc for Yul

docs/compile.md

@@ -3,16 +3,22 @@ Compiler (Solidity)
 
 Clicking the Solidity icon in the icon panel brings you to the Solidty Compiler.
 
-Compiling is triggered when you click the compile button ( **A. in image below**). If you want the file to be compiled each time the file is saved or when another file is selected - check the auto compile checkbox ( **B. in image below**).  
+Compiling is triggered when you click the compile button ( **D. in image below**). If you want the file to be compiled each time the file is saved or when another file is selected - check the auto compile checkbox ( **E. in image below**).
+
+Since the Solidity version `0.5.7`, it is possible to compile `Yul` files. Please read the (([solidity documentation about Yul]https://solidity.readthedocs.io/en/latest/yul.html)) which contain some code examples.
+You can use the language dropdown ( **B. in image below**) to switch the language. **This dropdown list is only available for versions greater than or equal to `0.5.7`.**
+
+The fork selection dropdown list ( **C. in image below**) allows to compile code against a specific ethereum hard fork. 
+The `compiler default` corresponds to the default hard fork used by a specific version. Please go to "Compilation Details" ( **G. in image below**) in the settings of `Metadata` section to see the harfork name used for the current compilation.
 
 If the contract has a lot of dependencies it can take a while to compile - so you use autocompilation at your discretion.
 
 ![](images/a-sol-compiler.png)
 
 After each compilation, a list is updated with all the newly compiled
-contracts.  The contract compiled can be selected with the Contract pulldown menu ( **C. in image below**).  Multiple contracts are compiled when one contract imports other contracts.  Selecting a contract will show information about that one.
+contracts.  The contract compiled can be selected with the Contract pulldown menu ( **F. in image below**).  Multiple contracts are compiled when one contract imports other contracts.  Selecting a contract will show information about that one.
 
-When the "Compilation Details" button is clicked ( **D. in image below**), a modal opens displaying detailed information about the current selected contract.
+When the "Compilation Details" button is clicked ( **G. in image below**), a modal opens displaying detailed information about the current selected contract.
 
 From this tab, you can also publish your contract to Swarm (only non
 abstract contracts can be published).