Checksum_Deprecation: tweak phrasing/explanation/etc

docs/Checksum_Deprecation.md

@@ -1,22 +1,18 @@
 # MD5 and SHA-1 Deprecation
 
-During early 2015 Homebrew started the process of deprecating _SHA1_ for package
-integrity verification. Since then every formulae under the Homebrew organisation
-has been moved onto _SHA256_ verification; this includes both source packages
-and our precompiled packages (bottles).
+In early 2015 Homebrew started the process of deprecating _SHA1_ for package
+integrity verification. Since then formulae under the Homebrew organisation
+have been moved onto using _SHA256_ for verification; this includes both source
+packages and our precompiled packages (bottles).
 
-We have stopped supporting _SHA1_ and _MD5_ entirely.
-_MD5_ checksums were removed from core formulae in 2012 but until April 2015
-if you tried to install a formula still using one Homebrew wouldn't actively stop you.
+Homebrew has since stopped supporting _SHA1_ and _MD5_ entirely.
+_MD5_ checksums were removed from core formulae in 2012 and as of April 2015
+installing a formula verified by _MD5_ is actively blocked.
 
 We removed _SHA1_ support in **November 2016**,
 21 months after we started warning people to move away from it for verification.
 This is enforced in the same way _MD5_ is, by blocking the installation of that
 individual formula until the checksum is migrated.
 
-From March 20th 2016 we've stepped up the visibility of that notification & you'll start
-seeing deprecation warnings when installing _SHA1_-validated formula.
-If you see these please consider reporting it to where the formula originated.
-
 This means custom taps, local custom formulae, etc need to be migrated to use
 _SHA256_ before you can install them.