Update README after history rewrite (OWASP#221)

BFG was used to rewrite the repo's history, dropping all the previous
assets/files/migrated content. The repo is now 211MB instead of over
5GB.

Signed-off-by: kingthorin <kingthorin@users.noreply.github.com>

README.md

@@ -1,3 +1,17 @@
+# 2020-July-02: Please Re-fork and Re-clone
+
+In order to greatly reduce the repository's size (from >5GB to ~211MB) we have had to re-write the repo's history. Please [delete your fork](https://docs.github.com/en/github/administering-a-repository/deleting-a-repository) and local clones. [Re-fork](https://docs.github.com/en/github/getting-started-with-github/fork-a-repo) and [re-clone](https://docs.github.com/en/github/creating-cloning-and-archiving-repositories/cloning-a-repository).
+
+This was done to make the repository more manageable for those not on high speed connections:
+
+Before:
+`Receiving objects: 100% (8604/8604), 5.27 GiB | 16.23 MiB/s, done.`
+
+After:
+`Receiving objects: 100% (4672/4672), 211.77 MiB | 17.10 MiB/s, done.`
+
+# General
+
 [OWASP Community Pages](https://owasp.org/www-community/) are a place where OWASP can accept community contributions for security-related content. To contribute, go to the repository for this site. Go into the pages folder and create a new file. Save and commit the file.
 
 Include the following front matter in your file (for examples, see pages/password-special-characters.md in this repository):