README: Set alt="" attributes.

README.md

@@ -15,17 +15,17 @@ them, particularly in catching syntax errors.
 
 Some examples:
 
-Before: [![Screenshot](images/before1-smaller.png)](images/before1.png)
+Before: [![Screenshot #1.1](images/before1-smaller.png)](images/before1.png)
 <br/>
-After:&nbsp; [![Screenshot](images/after1-smaller.png)](images/after1.png)
+After:&nbsp; [![Screenshot #1.2](images/after1-smaller.png)](images/after1.png)
 
-Before: [![Screenshot](images/before2-smaller.png)](images/before2.png)
+Before: [![Screenshot #2.1](images/before2-smaller.png)](images/before2.png)
 <br/>
-After:&nbsp; [![Screenshot](images/after2-smaller.png)](images/after2.png)
+After:&nbsp; [![Screenshot #2.2](images/after2-smaller.png)](images/after2.png)
 
-Before: [![Screenshot](images/before3-smaller.png)](images/before3.png)
+Before: [![Screenshot #3.1](images/before3-smaller.png)](images/before3.png)
 <br/>
-After:&nbsp; [![Screenshot](images/after3-smaller.png)](images/after3.png)
+After:&nbsp; [![Screenshot #3.2](images/after3-smaller.png)](images/after3.png)
 
 
 How to install