updated issue templates

Author: robertmartin8

.github/ISSUE_TEMPLATE/bug.md

@@ -13,8 +13,8 @@ A clear and concise description of what the bug is.
 **Expected behavior**
 A clear and concise description of what you expected to happen.
 
-**Screenshots**
-If applicable, add screenshots to help explain your problem.
+**Code sample**
+Add a minimal reproducible example (see [here](https://stackoverflow.com/help/minimal-reproducible-example)).
 
 **Operating system, python version, PyPortfolioOpt version**
 e.g MacOS 10.146, python 3.7.3, PyPortfolioOpt 1.2.6

.github/ISSUE_TEMPLATE/feature_request.md

@@ -10,8 +10,8 @@ assignees: ''
 **Is your feature request related to a problem?**
 A clear and concise description of what the problem is.
 
-**Describe the solution you'd like**
-A clear and concise description of what you want to happen.
+**Describe the feature you'd like**
+A clear description of the feature you want, or a link to the textbook/article describing the feature.
 
 **Additional context**
 Add any other context or screenshots about the feature request here.

.github/ISSUE_TEMPLATE/help-needed.md

@@ -10,5 +10,7 @@ assignees: ''
 **What are you trying to do?**
 Clear description of the problem you are trying to solve with PyPortfolioOpt
 
+**What have you tried?**
+
 **What data are you using?**
 What asset class, how many assets, how many data points. Preferably provide a sample of the dataset as a csv attachment.

.github/ISSUE_TEMPLATE/installation-error.md

@@ -16,5 +16,5 @@ pip install pyportfolioopt
 **Error message**
 
 ```
-Copy paste the terminal message here
+Copy paste the terminal message inside the backticks.
 ```