Add v5.0.0 to testnet version ordering (#87)

References:
https://linear.app/thesis-co/issue/TET-1802/the-v500-mezod-release-candidate-testnet

Here we update the version ordering for testnet to include the upcoming
v5.x.x release.

Author: tomaszslabon

README.md

@@ -103,7 +103,8 @@ Asterisk (*) denotes the latest minor/patch version.
 - `v1.0.0-rc1`: from block 3712500 to block 5559500
 - `v2.0.2`: from block 5559500 to block 5695000
 - `v3.*.*`: from block 5695000 to block 6853500
-- `v4.*.*`: from block 6853500 to the current chain tip
+- `v4.*.*`: from block 6853500 to block 8838000
+- `v5.*.*`: from block 8838000 to the current chain tip
 
 #### Version ordering for Mezo Mainnet