Improve code quality and add comments

frontend/src/app/Services/data.service.ts

@@ -17,6 +17,7 @@ export class DataService {
   ) {}
 
   /**
+   * Function to get all portfolio data
    * @returns Observable
    */
   public getStockData(): Observable<any> {
@@ -30,6 +31,7 @@ export class DataService {
   }
 
   /**
+   * Function to get all transaction data
    * @returns Observable
    */
   public getTransactionData(): Observable<any> {
@@ -43,6 +45,7 @@ export class DataService {
   }
 
   /**
+   * Function to create a transaction
    * @param  {string} symbol
    * @param  {Date} time
    * @param  {number} count
@@ -77,6 +80,7 @@ export class DataService {
   }
 
   /**
+   * Function to get all keywords
    * @returns Observable
    */
   public getKeywords(): Observable<any> {