update contributing guidelines (edent#356)

CONTRIBUTING.md

@@ -9,14 +9,14 @@ Thanks for submitting or fixing an icon! Here is a helpful guide to what you nee
 ## New File
 
 Filename should be `nameofservice.svg` - all in lower-case.
+If a special character must be used, please replace it with an underscore (no dot nor a dash).
 
 Place the file in `/images/svg/`
 
 At a minimum, your icon needs these components:
 
-```
-<svg
-xmlns="http://www.w3.org/2000/svg"
+```svg
+<svg xmlns="http://www.w3.org/2000/svg"
 aria-label="..." role="img"
 viewBox="0 0 512 512"><rect
 width="512" height="512"
@@ -26,6 +26,11 @@ fill="#fff"/>...</svg>
 
 Please keep the whitespace as-is. This makes viewing diffs easier. Please use UNIX line-endings `LF` rather than Windows-style `CRLF`.
 
+If you can, remove the end of line at the end of the file:
+* VIm: `:set noeol` (optionally `:set nofixendofline`)
+* perl: `perl -pi -e 'chomp if eof' $filename`
+* shell: `printf %s "$(cat $filename)" > filename-without-nl.svg`
+
 ### Guidelines
 
 This is the standard guideline. Use this to help with sizing your icons and they will look good no matter what border radius is chosen.
@@ -41,8 +46,8 @@ This is the standard guideline. Use this to help with sizing your icons and they
 
 Add a table cell to README.md - it must be in this format:
 
-```
-<td>Name of Service<br><img src="images/svg/nameofservice.svg" width="125" title="Name Of Service" /><br>123 Bytes</td>
+```html
+<td>Name of Service<br><img src="https://edent.github.io/SuperTinyIcons/images/svg/nameofservice.svg" width="125" title="Name Of Service"/><br>123 Bytes</td>
 ```
 
 Please add the correct file size.
@@ -54,7 +59,7 @@ Please add the correct file size.
 
 ## Reference Page
 
-* Edit the file `/images/reference/index.md`
+* Edit the file [`images/reference/index.md`](images/reference/index.md)
 * Add a link to the *official* style guide or brand guidelines.
 * For example `| <img src="/images/svg/nameofservice.svg" width="256" />	| <img src="/images/reference/nameofservice.jpg" width="256" />	| https://example.com/press |`