Update README for additional dependency required to render .png, add `make clean` to README, remove publish.sh

[evonnec]

• Update README for additional dependency required to render .png ImageMagick
• add make clean to README
• remove publish.sh and references to pub from Makefile as it's defunct

Without imagemagick installation:

GitHub/effectivescala(master⚡)» make all                                                                       [16:53:28]
cat effectivescala.mo | bash proc.sh | bash toc.sh | bash fmt.sh | peg-markdown --smart --notes > effectivescala.html
/opt/homebrew/bin/pic2graph: line 102: convert: command not found
/opt/homebrew/bin/pic2graph: warning: falling back to old '-crop 0x0' trim method
/opt/homebrew/bin/pic2graph: line 118: convert: command not found
cat header.html.inc effectivescala.html footer.html.inc > index.html
cat effectivescala-ja.mo | bash proc.sh | bash toc.sh | bash fmt.sh | peg-markdown --smart --notes > effectivescala-ja.html
/opt/homebrew/bin/pic2graph: line 102: convert: command not found
/opt/homebrew/bin/pic2graph: warning: falling back to old '-crop 0x0' trim method
/opt/homebrew/bin/pic2graph: line 118: convert: command not found
cat header-jp.html.inc effectivescala-ja.html footer-jp.html.inc > index-ja.html
cat effectivescala-ru.mo | bash proc.sh | bash toc.sh | bash fmt.sh | peg-markdown --smart --notes > effectivescala-ru.html
/opt/homebrew/bin/pic2graph: line 102: convert: command not found
/opt/homebrew/bin/pic2graph: warning: falling back to old '-crop 0x0' trim method
/opt/homebrew/bin/pic2graph: line 118: convert: command not found
cat header-ru.html.inc effectivescala-ru.html footer-ru.html.inc > index-ru.html
cat effectivescala-cn.mo | bash proc.sh | bash toc.sh | bash fmt.sh | peg-markdown --smart --notes > effectivescala-cn.html
/opt/homebrew/bin/pic2graph: line 102: convert: command not found
/opt/homebrew/bin/pic2graph: warning: falling back to old '-crop 0x0' trim method
/opt/homebrew/bin/pic2graph: line 118: convert: command not found
cat header-cn.html.inc effectivescala-cn.html footer-cn.html.inc > index-cn.html

GitHub/effectivescala(master⚡)» which convert                                                                  [16:53:30]
convert not found

After brew install imagemagick

GitHub/effectivescala(additional_tips)» which convert                                                           [17:11:45]
/opt/homebrew/bin/convert

make pub errors:

GitHub/effectivescala(master)» make pub                                                               [17:08:04]
./publish.sh index.html index-ja.html index-ru.html index-cn.html coll.png
Cloning into '/tmp/effectivescala.27222'...
[email protected]: Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
cp: /tmp/effectivescala.27222 is not a directory
./publish.sh: line 28: cd: /tmp/effectivescala.27222: No such file or directory
On branch master
Your branch is ahead of 'origin/master' by 1 commit.
  (use "git push" to publish your local commits)

nothing to commit, working tree clean
error: src refspec gh-pages does not match any
error: failed to push some refs to 'https://github.com/twitter/effectivescala.git'
make: *** [pub] Error 1
GitHub/effectivescala(master)» git status 

README.md.

# Effective Scala

This is the repository for the [Effective Scala](https://twitter.github.com/effectivescala/) document. 

It is "typeset" in [markdown](https://daringfireball.net/projects/markdown/) using [PEG markdown](https://github.com/jgm/peg-markdown). It also requires the [GNU Troff suite (groff)](https://www.gnu.org/software/groff/) and it requires [ImageMagick](https://imagemagick.org/script/download.php) to use pic2graph convert (https://imagemagick.org/script/convert.php)

## Building
To clean the space:

	`make clean`

To render the document:

	`make`

or:

	`make all`

## Contributing

Want to contribute and improve the guide? Have a bug or a question? 

Please create an issue here on GitHub: https://github.com/twitter/effectivescala/issues

## License

Copyright 2012 Twitter, Inc.

Licensed under the CC-BY 3.0: https://creativecommons.org/licenses/by/3.0