Update docs for Foundry Upgrades to v0.4.0 (#1120)

Author: ericglau

docs/modules/ROOT/pages/foundry/pages/foundry-upgrades.adoc

@@ -59,27 +59,25 @@ Follow the steps above, but instead of running `forge install OpenZeppelin/openz
 npm install @openzeppelin/foundry-upgrades
 ----
 
-Then add the following additional lines to `remappings.txt`, in addition to the ones described above:
+Then add the following additional line to `remappings.txt`, in addition to the ones described above:
 [source,console]
 ----
 openzeppelin-foundry-upgrades/=node_modules/@openzeppelin/foundry-upgrades/src/
-solidity-stringutils/=node_modules/@openzeppelin/foundry-upgrades/lib/solidity-stringutils/
 ----
 
 ==== Soldeer
 
 Follow the steps above, but instead of running `forge install OpenZeppelin/openzeppelin-foundry-upgrades`, use one of the install commands described in https://soldeer.xyz/project/openzeppelin-foundry-upgrades
 
-Then add the following additional lines to `remappings.txt`, in addition to the ones described above (replace `0.3.6` with the version of the plugin that you installed):
+Then add the following additional line to `remappings.txt`, in addition to the ones described above (replace `0.3.6` with the version of the plugin that you installed):
 [source,console]
 ----
 openzeppelin-foundry-upgrades/=dependencies/openzeppelin-foundry-upgrades-0.3.6/src/
-solidity-stringutils/=dependencies/openzeppelin-foundry-upgrades-0.3.6/lib/solidity-stringutils/
 ----
 
 == Foundry Requirements
 
-This library requires https://github.com/foundry-rs/forge-std[forge-std] version 1.8.0 or higher.
+This library requires https://github.com/foundry-rs/forge-std[forge-std] version 1.9.5 or higher.
 
 == Before Running