Clarify when to `make install_go` and when not to.

make install_go uses a PPA mentioned but not supported by Go. This PPA at present time seems poorly maintained (doesn't support anything beyond Focal/20.04) and really doesn't bring anything to the table since post-Bionic/18.04 versions already meet our minimum requirement of 1.11.

Fixes #449 (closed).

README.md

@@ -10,13 +10,11 @@ manually, or send us a patch.
   make build
 ```
 
-You need at least go 1.11. If you have something older and are using ubuntu, you can do:
+You need at least go 1.11. 
 
-```
-  make install_go
-```
+If you have Ubuntu Bionic/18.04, the package in the repositories is too old. To resolve this, you can do `make install_go`. Do not do this if you have a later version.
 
-For other situations, have a look at https://github.com/golang/go/wiki/Ubuntu or https://golang.org/dl/
+For other situations, have a look at https://github.com/golang/go/wiki#working-with-go
 
 ## Test
 
@@ -39,7 +37,7 @@ You need to have installed and added to your user PATH (mentioned version tested
 4) Cygwin64 (>= 2.905 64 bit)
 5) Using Cygwin `Package Select` window install `python3` and `make` packages. 
 
-**Note:** for #5 you don't need to add packages to PATH they will available in `cygwin` after installation.
+**Note:** for \#5 you don't need to add packages to PATH they will available in `cygwin` after installation.
 
 #### Get Source
 ```